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To understand the effects of nitrogen deposition on element cycling and nutrient limitation status in forest ecosystems, we examined the effects of nitrogen deposition on the stoichiometric characteristics of forest soil-microbial-extracellular enzymes in Pinus yunnanensis forest. We conducted a field experiment with control (CK, 0 g N·m -2 ·a -1 ), low nitrogen (LN, 10 g N·m -2 ·a -1 ), medium nitrogen (MN, 20 g N·m -2 ·a -1 ) and high nitrogen (HN, 25 g N·m -2 ·a -1 ) since 2019. We collected soil samples (0-5 cm, 5-10 cm and 10-20 cm) at September 2022, and measured the contents of soil organic, total nitrogen, total phosphorus, microbial biomass carbon, nitrogen and phosphorus (MBC, MBN, MBP) and the activities of C, N, and P acquisition enzymes. The results showed that nitrogen deposition significantly reduced soil organic content, C:N and C:P by 6.9%-29.8%, 7.6%-45.2% and 6.5%-28.6%, and increased soil total N content and N:P by 10.0%-45.0% and 19.0%-46.0%, respectively. Nitrogen addition did not affect soil total P content. Except for soil C:N and C:P, soil nutrient content and stoichiometric ratio were highest in 0-5 cm soil layer. MN and HN treatments significantly decreased MBN by 11.0%-12.7%. MBC, MBP, and their stoichiometry did not change significantly under nitrogen deposition. Soil microbial nutrient content in 0-5 cm soil layer was significantly higher than that in other soil layers. Nitrogen deposition significantly decreased the activities of cellobiose hydrolase and leucine aminopeptidase (decreased by 14.5%-16.2% and 48.7%-66.3%). HN treatment promoted β-1,4-glucosidase activity (increased by 68.0%), but inhibited soil enzyme stoichiometric carbon to nitrogen ratio and nitrogen to phosphorus ratio (decreased by 95.4% and 88.4%). LN and MN treatment promoted β-1,4-N-acetylglucosaminidase activity (increased by 68.3%-116.6%), but inhibited enzyme stoichiometric carbon to phosphorus ratio (decreased by 14.9%-29.4%). Alkaline phosphatase activity had no significant change. Soil enzyme activities were significantly decreased with increasing soil depth. Soil total N and total P and microbial nutrients were negatively correlated with vector angle (representing microbial nitrogen or phosphorus limitation), while vector length (representing microbial carbon limitation) was consistently significantly positively correlated with vector angle, suggesting the synergistic promotion between microbial carbon limitation and phosphorus limitation. Nitrogen deposition gradually shifted to phosphorus limitation while alleviating microbial nitrogen limitation in P. yunnanensis forest. In addition, microbial activities in this region was limited by C availability, and the relationship between microbial C and P limitation was proportional.

Studying the stoichiometric characteristics of soil nutrients aids in evaluating soil quality and deciphering the coupling of soil nutrients. The influence of migratory bird activities on the dynamics of wetland soil nutrients and their stoichiometric remains unclear. We classified the central, peripheral and adjacent natural grassy areas as severe, mild, and no bird activity (control), respectively, in Donghu Carex meadow, a representative migratory bird habitat in Poyang Lake, based on flock characteristics and initial surveys. We analyzed the contents and stoichio-metry of soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) across soil depths of 0-100 cm under different intensities of migratory bird activities. The results showed that the activities of migratory birds significantly impacted nutrient levels exclusively within 0-30 cm soil. Mild activities markedly enhanced SOC and TN across 0-30 cm soil, while both mild and severe activities significantly raised TP within the same depth. For the 0-100 cm soil profiles, soil C/N ratios were 10.0, 10.8, and 9.9, C/P ratios were 23.5, 30.0, and 22.7, and N/P ratios were 2.3, 2.7, and 2.3 under no, mild, and severe bird activities, respectively. Further, mild activities of migratory birds significantly increased soil C/N, C/P and N/P ratios only within the 0-30 cm depth, while the stoichiometric ratios of all soil layer had no significant difference under severe bird activity. Soil stoichiometric ratios strongly correlated with physicochemical properties. SOC, TN, and TP primarily mediated the effects of migratory bird activity on soil carbon, nitrogen, and phosphorus stoichiometric ratios in Poyang Lake wetland. In conclusion, the influence of migratory bird activity on the stoichiometric ratios of soil carbon, nitrogen, and phosphorus in Poyang Lake wetland exhibited depth threshold (approximately 30 cm), aligning with the "Intermediate Distur-bance Hypothesis". These findings could provide a new perspective for the protection of wetlands and migratory birds.

Warming drives material cycling in terrestrial ecosystems by affecting litter decomposition, as it can alter litter yield, quality and decomposer composition and activity. The effect of warming on the decomposition of mixed litter in arid and semi-arid zones remains unknown. We investigated the mass loss and nutrient release dynamics during 450 days of decomposition of Artemisia ordosica , Leymus secalinus , and their mixture in Mu Us Desert by open-top chambers and litter bags. The results showed interspecific differences in the responses to warming, in that warming promoted mass loss and N and P release from L. secalinus and inhibited mass loss and P but promoting N release from A. ordosica . Mixing of A. ordosica and L. secalinus litter inhibited decomposition. Warming enhanced the antagonistic effects of mixed decomposition. The total mass loss of mixed litter was decreased by 9%, and the release of N and P was decreased by 4.9% and 12.6%, respectively. The antagonistic effects of mixed litter mass loss and P release under the warming treatment gradually strengthened with time, with N release changing from a synergistic to an antagonistic effect at 150 d. The non-additive effects produced by the mixed decomposition of A. ordosica and L. secalinus litter were jointly regulated by temperature and time. Future research on mixed litter decomposition should consider the interaction between temperature and time.

Exploring nutrient limitation in forest soil holds significant implications for forest tending and management. However, current research on nutrient limitation status of microorganisms in Robinia pseudoacacia plantations within the Loess Plateau remains insufficient. To investigate soil microbial nutrient limitation of R. pseu-doacacia plantations on the Loess Plateau, we selected R. pseudoacacia plantations with different afforestation time series (15, 25, 35, and 45 years) and a pile of barren slope cropland (control) in Yongshou County, Shaanxi Province as the research objects. We analyzed the contents of soil organic matter, total nitrogen, and total phosphorus, and the activities of β-1,4-glucosidase (BG), cellobiose hydrolase (CBH), leucine aminopeptidase (LAP), β-1,4-N-acetylglucoside (NAG) and phosphatase (AP). We analyzed the soil nutrient limitation by stoichiometry and enzyme metrology. The results showed a shift in soil pH from alkaline to acidic during vegetation restoration process, and that total phosphorus exhibited a gradual decrease over the course of 0 to 25 years. Soil orga-nic matter, total nitrogen and enzyme activities exhibited an increasing trend during the same time frame. However, between 25 and 45 years of age, soil total phosphorus, soil organic matter, total nitrogen, AP and LAP gradually declined while NAG, BG, and CBH initially increased and then decreased. Notably, the values of (BG+CBH)/(LAP+NAG), (BG+CBH)/AP and (LAP+NAG)/AP in R. pseudoacacia plantations were higher than the global average throughout the process of vegetation restoration. In the study area, the vector length was less than 1 and gradually increased, indicating that a progressive increase in microbial carbon limitation during the process of vegetation restoration. The vector angle exceeded 45° and exhibited an overall decreasing trend, suggesting that soil microorganisms were constrained by phosphorus (P) with a gradual deceleration of P limitation, without any nitrogen (N) limitation. The restoration of R. pseudoacacia plantation resulted in significant change in soil physical and chemical properties, while the time series of afforestation also influenced nutrient limitation of soil microorganisms.

Vegetation restoration can effectively enhance soil quality and soil organic carbon (SOC) sequestration. In this study, the distribution characteristics of soil nutrients and SOC along soil profile (0-100 cm), and their responses to restoration years (16, 28, 38 years) were studied in Caragana korshinskii plantations in the southern mountainous area of Ningxia, compared with cropland and natural grassland. The results showed that: 1) the contents of SOC, soil total nitrogen (TN), total phosphorus (TP), particulate organic carbon (POC), mineral-associated organic carbon (MAOC) and the proportion of particulate organic carbon to total organic carbon (POC/SOC) all decreased with increasing soil depth. The ratio of mineral-associated organic carbon to total organic carbon (MAOC/SOC) exhibited an opposite trend. 2) The contents of SOC, TN, TP, C:P, N:P, POC and MAOC gra-dually decreased as the restoration years increased. However, the C:N ratio showed no significant change. The POC/SOC ratio initially increased and then decreased, while the MAOC/SOC ratio decreased initially and then increased. 3) In three different types of vegetation, POC, MAOC, and SOC showed a highly significant positive linear correlation, with the increase in SOC mainly depended on the increase in MAOC. The SOC, TN, TP, POC and MAOC contents in natural grassland and C. korshinskii plantations were significantly higher than those in cropland. In conclusion, soil nutrients and POC and MAOC contents of C. korshinskii plantations gradually decreased with the increases in restoration years. However, when compared with cropland, natural grassland and C. korshinskii plantations demonstrated a greater capacity to maintain and enhance soil nutrient and carbon storage.

To understand the effects of different stover mulching amounts in no-tillage on soil carbon and nitrogen contents and enzyme activities, finding a stover mulching amount which can meet the requirement of soil carbon and nitrogen accumulation while maximizing economic benefits, we conducted a long-term conservation tillage field experiment since 2007 in Mollisols area of Northeast China. We analyzed soil carbon and nitrogen contents, enzyme activities and economic benefits under conventional tillage (Control, CT), no-tillage without stover mulching (NT 0 ), no-tillage with 33% stover mulching (NT 33 ), no-tillage with 67% stover mulching (NT 67 ), and no-tillage with 100% stover mulching (NT 100 ) before planting in May 2020. The results showed that compared with CT, NT 0 did not affect soil organic carbon (SOC) and total nitrogen (TN) contents, but increased soil organic carbon recalcitrance and decreased the availability of dissolved organic nitrogen (DON) and ammonium nitrogen. Compared with NT 0 , no-tillage with stover mulching significantly increased SOC contents in 0-10 cm layer and increased with the amounts of stover. In addition, NT 67 and NT 100 significantly increased SOC stocks, facilitating the accumulation of soil organic matter. The effects of different stover mulching amounts on soil nitrogen content in 0-10 cm layer were different. Specifically, NT 33 increased DON content and DON/TN, NT 67 increased DON content, while NT 100 increased TN content. Compared with CT, NT 0 decreased peroxidase (POD) activity in 0-10 cm layer. Compared with NT 0 , NT 33 increased β-glucosidase (βG), cellobiase (CB), 1,4-β-N-acetylglucosaminidase (NAG), polyphenol oxidase (PPO) and POD activities, while NT 67 only increased CB, NAG and POD activities in 0-10 cm soil layer, both alleviated microbial nutrient limitation. NT 100 increased PPO activity in 10-20 cm layer. NT 33 increased carbon conversion efficiency of stover compared with NT 100 , and had the highest economic benefit. In all, no-tillage with 33% stover mulching was the optimal strategy, which could promote nutrient circulation, boost stover utilization efficiency, improve the quality of Mollisols, and maximize guaranteed income.

To explore the causes of red tides in Qinhuangdao coastal water, we conducted surveys on both water quality and red tides during April to September of 2022 and analyzed the relationships between main environmental factors and red tide organisms through the factor analysis and canonical correspondence analysis. The results showed that there were eight red tides along the coast of Qinhuangdao in 2022, with a cumulative blooming area of 716.1 km 2 . The red tides could be divided into three kinds based on the major blooming organisms and occurrence time, Noctiluca scintillans bloom, diatom-euglena ( Skeletonema costatum , Eutreptiella gymnastica , Pseudo-nitzschia spp.) bloom, and dinoflagellate ( Scrippsiella trochoidea and Ceratium furca ) bloom. Seasonal factor played roles mainly during July to September, while inorganic nutrients including nitrogen and phosphorus influenced the blooms mainly in April and July. The canonical correspondence analysis suggested that N. scintillans preferred low temperature, and often bloomed with high concentrations of ammonium nitrogen and dissolved inorganic phosphorus. S. costatum , E. gymnastica , and Pseudo-nitzschia spp. could tolerate broad ranges of various environmental factors, but favored high temperature and nitrogen-rich seawater. C. furca and S. trochoidea had higher survival rate and competitiveness in phosphate-poor waters. Combined the results from both analyses, we concluded that the causes for the three kinds of red tide processes in Qinhuangdao coastal areas in 2022 were different. Adequate diet algae and appropriate water temperature were important factors triggering and maintaining the N. scintillans bloom. Suitable temperature, salinity and eutrophication were the main reasons for the diatom-euglena bloom. The abundant nutrients and seawater disturbance promoted the germination of S. trochoidea cysts, while phosphorus limitation caused the blooming organism switched to C. furca and maintained the bloom hereafter.

The aim of this study was to reveal the stoichiometric characteristics of carbon, nitrogen and phosphorus in rhizosphere and non-rhizosphere soils of Pinus sylvestris var. mongolica in the Hulunbuir desert. We investigated the contents and stoichiometry of organic carbon, total nitrogen, and total phosphorus contents of rhizosphere and non-rhizosphere soils across different stand ages (28, 37 and 46 a) of P. sylvestris var. mongolica plantations, with P. sylvestris var. mongolica natural forest as the control. We analyzed the correlation between soils properties and soil stoichiometry. The results showed that rhizosphere effect significantly affected soil N:P, and stand age significantly affected soil organic carbon content in P. sylvestris var. mongolica plantation. Soil organic carbon content in plantation was significantly lower than that in natural forest. Soil organic carbon and total nitrogen contents of plantations in both rhizosphere and non-rhizosphere soils firstly decreased and then increased with increasing stand age, while total phosphorus firstly increased and then decreased in rhizosphere soils, and firstly decreased and then increased in non-rhizosphere soils. There was significant positive correlations between C:N and C:P in rhizosphere soils but not in non-rhizosphere soils, suggesting that higher synergistic rhizosphere soil N and P limitation. The mean N:P values of rhizosphere and non-rhizosphere soils were 4.98 and 8.40, respectively, indicating that the growth of P. sylvestris var. mongolica was restricted by soil N and the rhizosphere soils were more N-restricted. The C:N:P stoichiometry of rhizosphere and non-rhizosphere soils were significantly influenced by soil properties, with available phosphorus being the most important driver. The growth of P. sylvestris var. mongolica was limited by N in the Hulunbuir desert, and root system played an obvious role in enriching and maintaining soil nutrients. It was recommended that soil nitrogen should be supplemented appropriately during the growth stage of P. sylvestris var. mongolica plantation, and phosphorus should be supplemented appropriately according to the synergistic nature of nitrogen and phosphorus limitation.

Forest type and stand age are important biological factors affecting soil enzyme activities. However, the changes in soil enzyme activities across stand ages and underlying mechanisms under the two forest restoration strate-gies of plantations and natural secondary forests remain elusive. In this study, we investigated the variations of four soil enzyme activities including cello-biohydrolase (CBH), β-1,4-glucosidase (βG), acid phosphatase (AP) and β-1,4-N-acetylglucosaminidase (NAG), which were closely associated with soil carbon, nitrogen, and phosphorus cycling, across Cunninghamia lanceolata plantations and natural secondary forests (5, 8, 21, 27 and 40 years old). The results showed that soil enzyme activities showed different patterns across different forest types. The acti-vities of AP, βG and CBH in the C. lanceolata plantations were significantly higher than those in the natural secon-dary forests, and there was no significant difference in the NAG activity. In the plantations, AP activity showed a decreasing tendency with the increasing stand ages, with the AP activity in the 5-year-old plantations significantly higher than other stand ages by more than 62.3%. The activities of NAG and CBH decreased first and then increased, and βG enzyme activity fluctuated with the increasing stand age. In the natural secondary forests, NAG enzyme activity fluctuated with the increasing stand age, with that in the 8-year-old and 27-year-old stand ages being significantly higher than the other stand ages by more than 14.9%. βG and CBH enzyme activities increased first and then decreased, and no significant difference was observed in the AP activity. Results of the stepwise regression analyses showed that soil predictors explained more than 34% of the variation in the best-fitting models predicting soil enzyme activities in the C. lanceolata plantations and natural secondary forests. In conclusion, there would be a risk of soil fertility degradation C. lanceolata plantations with the increasing stand age, while natural secondary forests were more conducive to maintaining soil fertility.

Under the context of global climate change and growing population, irrigation and fertilization have become important ways to ensure food production, with consequences on water cycling, energy flow, and materials cycling in terrestrial ecosystems. In the land surface model (LSM), coupling irrigation and fertilization schemes are of great importance for clearly understanding the land-atmosphere interactions to ensure food security. We reviewed the expression methods of three key parameters, namely, the applied method, usage, and time in the parameterization process of irrigation and fertilization (nitrogen fertilizer) in LSM. We found that the ways to irrigate and ferti-lize in LSM are different from the ways used in actual practice due to the limitation of the high resolution of spatio-temporal data, which makes it difficult to understand the actual influences of irrigation and fertilization on grain yield, environment, and local climate. Finally, we proposed future works: 1) taking the differences of crop water demand into account and making the different irrigation thresholds for different crops to properly evaluate the total and intensity of water consumption of different crops; 2) using the field records and the regional grid data of fertilization and irrigation developed in recent years to develop parameterized schemes that are more in line with actual agricultural operations, which can accurately reveal their economic, ecological, and climatic effects; 3) developing fertilization diagnosis scheme considering crop type, phenological stage, and soil basic fertility as the supplementary scheme in LSM, to improve the applicability and simulation accuracy of LSM in the areas without nitrogen fertilizer data.

To explore the coupling of dry-wet seasonal variations of soil respiration with their environmental factors in the alpine meadow under the background of increasing nitrogen (N) deposition, we conducted an experiment in the typical degraded Poa pratensis meadow in the Napahai, Yunnan. There were four treatments, i.e ., control (0 g·m -2 ·a -1 ), low (5 g·m -2 ·a -1 ), medium (10 g·m -2 ·a -1 ), and high (15 g·m -2 ·a -1 ) levels. We examined the effects of aboveground biomass, plant diversity, and soil physicochemical properties on soil respiration. The results showed that N deposition significantly promoted soil respiration. Compared with that in the control, soil respiration rates increased by 21.9%-53.9% and 27.3%-51.2% in dry and wet seasons, respectively. The maximum value of soil respiration rate was recorded in the medium N treatment. N deposition dramatically elevated aboveground biomass (52.2%-66.4%). Plant diversity declined with increasing N addition levels, with the maximum value (13.5%-24.2%) being recorded in high treatment in wet season. The values of ammonium nitrogen, organic matter, microbial biomass carbon and nitrogen, temperature and moisture in the three N treatments were elevated by 14.3%-333.5% compared with the control, while those of soil pH were decreased by 9.0%-34.6%. Results of the structural equation modelling showed that plant biomass, Shannon diversity, microbial biomass, soil temperature, and moisture showed a positive effect on soil respiration, while bulk density had a negative effect. Soil nitrogen pool and pH were main factors driving soil CO 2 emissions, accounting for 55.7% and 45.1% of the variations, respectively. Therefore, short-term atmospheric N deposition stimulated soil respiration primarily via altering soil pH and nitrogen pool components in the degraded alpine meadow.

Soil respiration is a key process in forest biogeochemical cycling. Exploring the relationship between plant functional traits and soil respiration can help understand the effects of tree species conversion on soil carbon cycling. In this study, we selected 15 common subtropical tree species planted in the logging site of second-generation Chinese fir forest to measure soil CO 2 emission fluxes, soil physicochemical properties, leaf and root functional traits of each species, and explored the effects of plant functional traits on soil respiration. The results showed that the annual flux of soil CO 2 emissions varied from 7.93 to 22.52 Mg CO 2 ·hm -2 , with the highest value under Castanopsis carlesii (22.52 Mg CO 2 ·hm -2 ) and the lowest value under Taxus wallichiana (7.93 Mg CO 2 ·hm -2 ). Results of stepwise regression analysis showed that the annual flux of soil CO 2 emission decreased with the increases of leaf nitrogen content and fine root diameter, and increased with increasing leaf non-structural carbohydrate. In the structural equation model, leaf non-structural carbohydrate had a direct and significant positive effect on soil CO 2 emission fluxes, while leaf nitrogen content and fine root diameter had a direct negative effect by decreasing soil pH and soluble organic nitrogen content. Plantations of different tree species would affect soil CO 2 emission directly by changing functional traits related to water and nutrient acquisition or indirectly through soil properties. When creating plantations, we should select tree species based on the relationship between plant functional traits and ecosystem functions, with a view to improving forest productivity and soil carbon sequestration potential.

Exploring the resource limitation of soil microbial metabolism is essential to understand ecosystem functions and processes. However, the spatially divergent patterns and drivers of soil microbial nutrient limitation cha-racteristics in montane ecosystems at small scales, especially at the slope aspect scale, are still unclear. In this study, we measured soil enzyme activities involved in carbon (C), nitrogen (N) and phosphorus (P) cycle and quantified the microbial nutrient limitations by enzyme stoichiometry in two representative mountain sites in subalpine region of western Sichuan, including the sunny and shady slopes with different vegetation types (shrubland and forest, respectively) in Miyaluo of Lixian County, and with the same vegetation type (shrubland) in Yakexia of Heishui County. The results showed that soil enzyme activities and their stoichiometric ratios were significantly different between slope aspects in Miyaluo, while the differences were not significant in Yakexia. The stoichiometry ratio of C-, N- and P-acquiring enzymes on the sunny slope of Miyaluo was 1:0.96:0.92, approaching the 1:1:1 ratio at the global scale, but deviated from 1:1:1 on the shady slope of Miyaluo (1:1.39:0.75) and the different slopes of Yakexia (1:1.09:1.35). There was no significant difference in vector length between slope aspects at both sites, indicating no significant effect of slope aspect on the microbial C limitation. The vector angle was significantly higher on the sunny slope (43.6°) than that on the shady slope (28.7°) in Miyaluo, suggesting that the microorganisms were mainly N-limited. Partial least squares path model showed that the vector angle was mainly directly influenced by the soil nutrient ratios. The vector angle ranged from 50.3° to 51.4°, and did not differ between slope aspects in Yakexia. Therefore, differences in vegetation types between slope aspects drove variations in soil enzyme activity and microbial nutrient limitation through soil properties. It would provide a scientific basis for predicting the spatial pattern of soil enzyme activity and microbial nutrient limitation.

In this study, we analyzed the vertical distribution characteristics of root biomass density, root length density, root surface area density in monoculture and mixture of Pinus tabuliformis and Robinia pseudoacacia plantations in Caijiachuan small watershed of Jixian County, Shanxi. We examined their relationships with soil physical and chemical properties in different stand types. The results showed that the total root biomass density of P. tabuliformis and R. pseudoacacia in mixture was more than 75% higher than that in monoculture. Root system of P. tabuli-formis mainly distributed in shallow layer (0-40 cm), while that of R. pseudoacacia was deeper (40-80 cm). Fine roots were predominant in different diameter classes. Length density and surface area density of fine roots were in the order of R. pseudoacacia in mixture > P. tabuliformis in mixture > R. pseudoacacia stand > P. tabuliformis stand. Root biomass density of fine roots was in the order of P. tabuliformis in mixture ＞ R. pseudoacacia in mixture ＞ P. tabuliformis stand ＞ R. pseudoacacia stand. In vertical profile, the total root and fine root biomass, root length and root surface area density of P. tabuliformis stand, R. pseudoacacia stand, P. tabuliformis in mixture and R. pseudoacacia in mixture showed a rule of decreasing with the increases of soil depth. Under different stand types, fine root length density, root biomass density and total root length density were positively correlated with soil total nitrogen, soil organic carbon, and soil water contents. Total root surface area density was significantly positively correlated with soil organic carbon, soil water content, and soil total nitrogen. The distribution of roots in pure and mixed stands of P. tabuliformis and R. pseudoacacia showed different patterns. Compared with the pure stand, the mixed stand had higher root biomass, soil nutrient contents, and soil water content.

We explored the relationship between climate factors (mean annual precipitation and mean annual temperature) and the contents and stoichiometry of soil carbon (C), nitrogen (N), and phosphorus (P) at different soil depths (0-5, 5-10, 10-20, 20-30, 30-50, 50-70, and 70-100 cm) temperate steppe of Longzhong. The results showed with the increases of soil depth, soil C, N contents, C:P, and N:P gradually decreased from 21.88 g·kg -1 , 1.84 g·kg -1 , 33.6 and 3.1 to 7.67 g·kg -1 , 0.59 g·kg -1 , 12.5 and 1.0, respectively. Soil C:N showed an increasing trend from 12.2 to 13.9, while soil P content remained stable with an average of 0.61 g·kg -1 . Soil C, N, C:P, and N:P were significantly positively correlated with mean annual precipitation and negatively correlated with mean annual temperature. Soil P content and C:N were not correlated with mean annual precipita-tion and mean annual temperature. With the increases of soil depth, the total explanatory power of the changes in soil C, N and P contents by mean annual precipitation and mean annual temperature decreased and then increased, and that in soil C:P, N:P and C:N did not change significantly. The changes of soil C, N and P contents on the temperature steppe were mainly influenced by mean annual precipitation. The effects and relative contributions of mean annual precipitation and mean annual temperature on the variations of soil nutrient contents and stoichiometry of C, N and P differed at different soil depths.

The southern mountainous areas in Ningxia are representative regions of the Loess Plateau, with extremely fragile ecological environment. Large area of pure plantations established during the project of Grain for Green has suffered from poor nutrient availability and biodiversity loss, while planting mixed plantations is commonly consi-dered as an effective way to improve the ecological benefits. We selected Robinia pseudoacacia + Picea asperata mixed plantation, R. pseudoacacia + Armeniaca sibirica mixed plantation, A. sibirica pure plantation and R. pseudoa-cacia pure plantation located ina Ningnan mountainous area as test objects. Based on the theory and method of ecological stoichiometry, we measured the C, N and P contents of leaves, litter and fine roots to understand nutrient cycling characteristics of different plantations. The results showed that there was significant difference in foliar stoichiometry of each tree species within the four plantations. P. asperata leaves had the highest C content in the R. pseudoacacia + P. asperata mixed plantation, and R. pseudoacacia leaves had the highest N and P contents in the R. pseudoacacia + A. sibirica mixed plantation. N content of R. pseudoacacia and A. sibirica leaves was significantly higher in mixed plantation compared with that in pure plantation. There was no significant difference in litter biomass, litter C, N, P contents and stoichiometric ratios between the pure and mixed plantations of R. pseudoacacia . Litter biomass in A. sibirica pure plantation was significantly higher than that in R. pseudoacacia + A. sibirica mixed plantation, while litter C content was significantly lower than that in the mixed plantation. Fine root biomass decreased with increasing soil depth in the four plantations, with total fine root biomass being the highest in the R. pseudoacacia + A. sibirica mixed plantation. N content and N:P of fine roots in the R. pseudoacacia + A. sibirica mixed plantation were higher than those in R. pseudoacacia and A. sibirica pure plantations. There was significant negative correlation between N content in leaves and fine roots of R. pseudoacacia + A. sibirica mixed plantation. There were significant negative correlations between the N content of leaves and litter, as well as between the P content of leaves and fine roots in the R. pseudoacacia + P. asperata mixed plantation. P content between litter and fine roots in A. sibirica pure plantation was significantly negatively correlated. Nutrient status of mixed plantations was better than pure plantations in the Ningnan mountainous area, with the mixed plantation of R. pseudoacacia and A. sibirica being the best. Mixed planting reduced nutrient limitation on plant growth to a certain extent.

Urease inhibitors and nitrification inhibitors can enhance nitrogen (N) fertilizer utilization efficiency and reducing N losses through regulating urea-N transformation. Common urease or nitrification inhibitors, however, are predominantly chemically synthesized and high-cost. Furthermore, their inhibitory effects are mediated by soil pro-perties, climatic conditions, and crop systems. In this study, we conducted a field experiment using natural synergists humic acid/zeolite, along with chemical nitrification inhibitor dicyandiamide (DCD) and their combination to elucidate the impacts of natural synergists combined with chemical inhibitors on annual yield, nitrogen utilization efficiency, soil nitrate-N accumulation, and nitrogen balance within the wheat/maize rotation system. The treatments included no nitrogen fertilizer application (CK), single application of urea (N), urea +DCD (ND), urea + humic acid (NH), urea + zeolite (NP), urea + urease inhibitor N-butylthiophosphoric triamide + DCD (NUD), urea + humic acid + DCD (NHD), and urea + zeolite + DCD (NPD). The results showed that, compared to the treatments NH and NP, the integration of humic acid or zeolite with DCD (NHD and NPD) significantly increased maize yield (11268 and 11397 kg·hm -2 ) and total annual yield (20494 and 20582 kg·hm -2 ), which were comparable to those of combined chemical urease and nitrification inhibitors (NUD). The NHD and NPD treatments had higher nitrogen utilization efficiency and lower soil nitrate-N accumulation in 80-100 cm soil layer across all seasons relative to the N treatment, which had no significant difference compared to the NUD treatment. Furthermore, a decline in soil nitrogen surplus by 10.7% and 13.9% was observed when comparing the NHD and NPD treatments with the NH and NP treatments, respectively. These findings suggested that combined humic acid or zeolite and chemical nitrification inhibitors could effectively enhance crop yield and N utilization efficiency and meet the requirements of the green and environmental preservation of modern agriculture.

The rhizosphere effect of plants affects soil organic carbon (SOC) mineralization. It is still unclear for the mechanism by which the rhizosphere effect of dominant plants in secondary broadleaved forest habitats invaded by moso bamboo affects SOC mineralization. Taking broadleaved tree species ( Quercus glauca and Cunninghamia lanceolata ) and moso bamboo, dominating respectively in uninvaded secondary broadleaved forest and bamboo forest formed after the invasion as test materials, we investigated rhizosphere effect of plants on the SOC mineralization in laboratory incubation experiments. The results showed that carbon mineralization rates of Phyllostachys edulis (PE), Quercus glauca (QG) and Cunninghamia lanceolata (CL) rhizosphere soils were 20%, 26%, and 21% higher than bulk soils, respectively. Carbon mineralization of bulk soils of QG and CL was 22% and 26% higher, while that of rhizosphere soils was 14% and 11% higher than PE, respectively. The contents of water-soluble organic carbon and organic carbon in rhizosphere soils of the three species were significantly higher than those of bulk soil, and the abundance of rhizosphere soil bacteria was higher than that of non-rhizosphere. The contents of microbial biomass carbon, water-soluble organic carbon, and total nitrogen were important factors influencing carbon mineralization in rhizosphere, while water-soluble organic carbon and microbial metabolic quotient were important factors influencing carbon mineralization in non-rhizosphere. On the whole, the rhizosphere effect increased total SOC mineralization, driving by changes in microbial biomass carbon, water-soluble organic carbon, and total nitrogen content. The results could provide a theoretical basis for plant-soil interaction on soil carbon cycling in bamboo invasion habitats.

Chlorophyll a (Chla) and diatom community structure are two indicators of lake water quality. In this study, we investigated the environmental parameters, chlorophyll a, and diatom community of four small urban lakes in Kunming (Beitan, Beihu, Nanhu and Longtan lakes in the campus of Yunnan Normal University) between March 2017 and December 2019. The results showed that the concentrations of total nitrogen (TN), total phosphorus (TP), and Chla in the four lakes showed significant seasonal fluctuation. The Chla concentration in Nanhu Lake, which had the highest nutrient level among the four lakes, was significantly higher than that in the other three lakes and largely affected by TN. In comparison, water temperature significantly contributed to the increases in Chla concentration in the other three lakes. Water temperature and TN were significantly correlated with Chla across the four lakes. Diatom assemblages in Beitan, Nanhu, and Longtan lakes were dominated by planktonic diatoms, and benthic diatoms were dominant in the shallowest lake Beihu, suggesting that water depth significantly affected the proportion of planktonic diatoms and dominant taxa. Water depth, TN, TP, transparency, and water temperature affected the spatio-temporal changes of diatom community structure, with water temperature as the major factor in causing the seasonal variation in diatom community, and TN and TP as the major drivers for community variation among lakes within the same season.

We assessed the seasonal dynamics of N 2 O emission in ant nests soils in secondary tropical Millettia leptobotrya forest of Xishuangbanna by using the static chamber-gas chromatography method, and determined the lin-kages between ant-mediated changes in soil properties ( e.g. , carbon pool, nitrogen pool, and temperature and humidity) and N 2 O emission. The results showed that ant nesting significantly affected soil N 2 O emission. The ave-rage soil N 2 O emission (0.67 mg·m -2 ·h -1 ) in ant nests was 40.2% higher than that in the control (0.48 mg·m -2 ·h -1 ). N 2 O emission in ant nests and the control showed substantial seasonal variation, with higher rate in June (0.90 and 0.83 mg·m -2 ·h -1 , respectively) than that in March (0.38 and 0.19 mg·m -2 ·h -1 , respectively). Ant nesting significantly increased the values (7.1%-74.1%) of moisture, temperature, organic carbon, total nitrogen, hydrolytic nitrogen, ammonium nitrogen, nitrate nitrogen, and microbial biomass carbon, but decreased pH (9.9%) compared with the control. Results of structural equation model showed that soil N 2 O emission was promoted by soil C and N pool, temperature, and humidity, but was inhibited by soil pH. The explained extents of soil nitrogen pool, carbon pool, temperature and humidity, and pH for N 2 O emission changes were 37.2%, 27.7%, 22.9% and 9.4%, respectively. Therefore, ant nesting regulated N 2 O emission dynamics by changing nitrification and denitrification substrates ( e.g ., nitrate and ammoniacal nitrogen), carbon pool, and micro-habitat (temperature and moisture) of soil in the secondary tropical forest.

To evaluate soil quality status of forest, grassland, and cropland in the southern and northern Tibetan Plateau, and to clarify the key influencing factors of productivity levels under three land use types, we measured the basic physical and chemical properties of 101 soil samples collected in the northern and southern Qinghai-Tibet Plateau. Principal component analysis (PCA) was used to select three indicators as the minimum data set (MDS) to comprehensively evaluate soil quality of the southern and northern Qinghai-Tibet Plateau. The result showed that soil physical and chemical properties of the three land use types were significantly different in the north and south. The contents of soil organic matter (SOM), total nitrogen (TN), available phosphorus (AP) and available potassium (AK) in the north were higher than those in the south, while the contents of SOM and TN of forest were signi-ficantly higher than those of cropland and grassland in both the north and south. Soil ammonium (NH 4 + -N) content showed a pattern of cropland > forest > grassland, with significant difference in the south. Soil nitrate (NO 3 - -N) content in the north and south was the highest in the forest. Soil bulk density (BD) and electrical conductivity (EC) of cropland were significantly higher than those of grassland and forest, and that of cropland and grassland in the northern part was higher than that of southern part. Soil pH of grassland in the south was significantly higher than that of forest and cropland, and that of forest was the highest in northern part. The selected indicators for eva-luating soil quality in the north were SOM, AP, and pH, and soil quality index of forest, grassland, and cropland was 0.56, 0.53 and 0.47. The selected indicators were SOM, total phosphorus (TP), and NH 4 + -N in the south, and soil quality index of grassland, forest and cropland was 0.52, 0.51 and 0.48, respectively. There was a significant correlation between soil quality index obtained by the total data set and the minimum data set, and the regression coefficient was 0.69. Soil quality in the north and south of the Qinghai-Tibet Plateau were grade Ⅲ, and soil organic matter was the main indicator limiting soil quality in this area. Our results provide a scientific basis for eva-luating soil quality and ecological restoration in the Qinghai-Tibet Plateau.

We examined the effects of freeze-thaw cycles (0, 1, 3, 5, 7, 15 cycles) on the activities of urease, invertase, and proteinase in the different layers of the soil under the four typical stands in the cold temperate zone, i.e ., Pinus pumila stand, Rhododendron-Betula platyphylla stand, Rhododendron-Larix gmelinii stand, Ledum-Larix gmelinii stand, with the indoor freeze-thaw simulation culture method being used. The relationship between soil enzyme activity and multiple physicochemical variables was analyzed during freeze-thaw alternation. The results showed that the activity of soil urease was firstly increased and then inhibited during freeze-thaw alternation. After freeze-thaw, urease activity did not differ from that without freeze-thaw. Invertase activity was firstly inhibited and then increased during freeze-thaw alternation, and was significantly increased by 8.5%-40.3% after freeze-thaw. Proteinase activity was firstly increased and then inhibited during freeze-thaw alternation, and was significantly decreased by 13.8%-68.9% after freeze-thaw. After freezing and thawing, there was significant positive correlation between urease activity and ammonium nitrogen and soil water content in Ledum-L. gmelinii stand and P. pumila stand, respectively, and proteinase activity had significant negative correlation with inorganic nitrogen concentration in P. pumila stand, Rhododendron-B. platyphylla stand, and Ledum-L. gmelinii stand. Invertase activity had significant positive correlation with organic matter in Rhododendron-L. gmelinii stand and Ledum-L. gmelinii stand.

To improve the utilization efficiency of nutrients and water and determine the best drip irrigation frequency for long-season tomato cultivation in solar greenhouses, we cultivated tomato grafted seedlings in soil using an integrated water and fertilizer technology: drip irrigation under mulch. Seedlings drip-irrigated with balanced fertilizer (containing 20% N, 20% P 2 O 5 , and 20% K 2 O) and high-K fertilizer (containing 17% N, 8% P 2 O 5 , and 30% K 2 O) once every 12 days were set as control (CK) and that with water once every 12 days as CK 1 , while other seedling groups, drip-irrigated with a nutrient solution of Yamazaki (1978) formula for tomato, were set as treatments (T 1 -T 4 ). There were four drip-irrigation frequencies, i.e ., once every 2 days (T 1 ), 4 days (T 2 ), 6 days (T 3 ), or 12 days (T 4 ), who received the same total amounts of fertilizer and water over the 12 experimental days. The results showed that, with the decreases of drip irrigation frequency, tomato yield, the accumulation of N, P and K in plant dry matter, the fertilizer partial productivity, and the nutrient utilization rate first increased and then decreased, peaking at the T 2 treatment. Compared with CK, under the T 2 treatment, plant dry matter accumulation and the accumulation of N, P and K increased by 4.9%, 8.0%, 8.0%, 16.8%, the partial productivity of fertilizer and the utilization efficiency of water increased by 142.8% and 12.2%, the use efficiency of N, P and K was better than CK by 241.4%, 466.6% and 235.9%, respectively, and the tomato yield increased by 12.2%. Under the experimental conditions, drip irrigation with the Yamazaki nutrient solution at a frequency of 4 days could increase the tomato yield, as well as the use efficiency of nutrients and water. Under long-season cultivation, these trends would result in considerable saving of water and fertilizer. Overall, our findings provided a basis for improving the scientific management of water and fertilizers under long-season tomato cultivation in protected facilities.

Aiming at solving the problems of soil environment deterioration and the decline of both yield and quality caused by excessive application of chemical fertilizer, we investigated the effects of rotted corn straw on the soil environment of root zone, yield and quality of cucumber with 'Jinyou 35' cucumber as the experimental material. There were three treatments, namely, combined application of rotted corn straw and chemical fertilizer (T 1 , the total nitrogen fertilizer application were 450 kg N·hm -2 , of which 9000 kg·hm -2 rotted corn straw was used as the subsoil fertilizer, and the rest was supplemented with chemical fertilizer), pure chemical fertilizer (T 2 , the total nitrogen fertilizer application was the same as T 1 ) and no fertilization (control). The results showed that the content of soil organic matter in root zone soil in T 1 treatment was much higher, but no difference between T 2 treatment and the control, after two continuous plantings in one year. The concentrations of soil alkaline nitrogen, available phosphorus, available potassium of T 1 and T 2 in cucumber root zone were higher than that in the control. T 1 treatment had lower bulk density, but markedly higher porosity and respiratory rate than T 2 treatment and the control in root zone soil. The electric conductivity of T 1 treatment was higher than that of the control, but significantly lower than T 2 treatment. There was no significant difference in pH among the three treatments. The quantity of bacteria and actinomycetes in cucumber rhizosphere soil were the highest in T 1 , and the lowest in the control. However, the highest quantity of fungi was found in T 2 . The enzyme activities of rhizosphere soil in T 1 treatment were markedly higher than those of the control, whereas those of T 2 treatment were significantly lower or had no significant difference relative to the control. The cucumber root dry weight and root activity of T 1 were significantly higher than that of the control. The yield of T 1 treatment increased by 10.1%, and fruit quality improved obviously. The root activity of T 2 treatment was also significantly higher than that in the control. There was no significant difference in root dry weight and yield between T 2 treatment and the control. Furthermore, T 2 treatment revealed a decrease in fruit quality relative to T 1 treatment. These results suggested that the combined application of rotted corn straw and chemical fertilizer could improve soil environment, promote root growth, enhance root activity and improve yield and quality of cucumber in solar-greenhouse, which could be popularized and applied in protected cucumber production.

We compared the interspecific differences in leaf nutrient resorption of two dominant understory species ( Lophatherum gracile and Oplimenus unulatifolius ), and analyzed the correlations between the intraspecific efficiency of leaf nutrient resorption and nutrient properties of soil and leaves in Chinese fir plantation. The results showed high soil nutrient heterogeneity in Chinese fir plantation. Soil inorganic nitrogen content and available phosphorus content varied from 8.58 to 65.29 mg·kg -1 and from 2.43 to 15.20 mg·kg -1 in the Chinese fir plantation, respectively. The soil inorganic nitrogen content in O. undulatifolius community was 1.4 times higher than that in L. gra-cile community, but there was no significant difference in soil available phosphorus content between the two communities. Both leaf nitrogen and phosphorus resorption efficiency of O. unulatifolius was significantly lower than that of L. gracile under the three measurement bases of leaf dry weight, leaf area, and lignin content. Resorption efficiency in L. gracile community expressed on leaf dry weight was lower than that expressed on leaf area and lignin content, while resorption efficiency expressed on leaf area was the lowest in O. unulatifolius community. The intraspecific resorption efficiency was significantly correlated with leaf nutrient contents, but was less correlated with soil nutrient content, and only the nitrogen resorption efficiency of L. gracile had significant positive correlation with soil inorganic nitrogen content. The results indicated that there was significant difference in the leaf nutrient resorption efficiency between the two understory species. Soil nutrient heterogeneity exerted a weak effect on the intraspecific nutrient resorption, which might be attributed to high soil nutrient availability and potential disturbance from canopy litter in Chinese fir plantation.

In this study, we sampled leaves of coniferous species Pinus koraiensis and broad-leaved tree species Fraxinus mandshurica from four latitudes in northeastern China to investigate the carbon (C), nitrogen (N), phosphorus (P) stoichiometric characteristics and nutrient resorption efficiency and their potential relationships, as well as their responses to climatic and edaphic factors. The results showed that stoichiometric characteristics were species-specific, and that the C and N contents in leaves of F. mandshurica significantly increased with increasing latitude. The C:N of F. mandshurica and N:P of P. koraiensis were negatively correlated with latitude, but an inverse relationship was found for N:P of F. mandshurica . P resorption efficiency was significantly correlated with latitude in P. koraiensis . The spatial variation of ecological stoichiometry of these two species was mainly affected by climatic factors such as mean annual temperature and precipitation, while that of nutrient resorption was influenced by several soil factors such as soil pH and nitrogen content. Principal component analysis showed that P resorption efficiency of P. koraiensis and F. mandshurica was significantly negatively correlated with N:P, but positively correlated with P content. N resorption efficiency showed significantly positive correlation with P content but negative correlation with N:P in P. koraiensis . Compared with P. koraiensis , F. mandshurica was more inclined to fast investment and return in terms of leaf traits.

Conservation tillage is an important management practice to guarantee soil fertility in degraded Mollisols. It is still unclear, however, whether the improvement and stability of crop yield under conservation tillage can be sustainable with increasing soil fertility and reducing fertilizer-N application. Based on a long-term tillage experiment initiated in Lishu Conservation Tillage Research and Development Station by Chinese Academy of Sciences, we conducted a 15 N tracing field micro-plot experiment to investigate the effects of reducing nitrogen application on maize yield and fertilizer-N transformation under long-term conservation tillage agroecosystem. There were four treatments, including conventional ridge tillage (RT), no-tillage with 0% (NT0), 100% (NTS) maize straw mul-ching, and 20% reduced fertilizer-N plus 100% maize stover mulching (RNTS). The results showed that after a complete cultivation round, the average percentages of fertilizer N recovery in soil residues, crop usage, and gaseous loss were 34%, 50%, and 16%, respectively. Compared with conventional ridge tillage, no-tillage with maize straw mulching (NTS and RNTS) significantly increased the use efficiency of fertilizer N in current season by 10% to 14%. From the perspective of N sourcing analysis, the average percentage of fertilizer N absorbed by crop parts (including seeds, straws, roots, and cobs) to the total N uptake reached nearly 40%, indicating that soil N pool was the main source of N for crop uptakes. In comparison with conventional ridge tillage, conservation tillage significantly increased total N storage in 0-40 cm by reducing soil disturbance and increasing organic inputs, and thus ensured the expansion and efficiency increment of soil N pool in degraded Mollisols. Compared with conventional ridge tillage, NTS and RNTS treatments significantly increased the maize yield from 2016 to 2018. In all, by improving fertilizer nitrogen utilization efficiency and maintaining the continuous supply of soil nitrogen, long-term management of no-tillage with maize straw mulching could achieve a stable and increasing maize yield in three consecutive growing seasons and simultaneously reduce environmental risks derived by fertilizer-N losses, even under the condition of 20% reduction of fertilizer-N application, and thus actualize the sustainable development of agriculture in Mollisols of Northeast China.

The implementation of ecological engineering projects such as "Green for Grain" causes great changes in the cycling and stoichiometry of soil carbon (C), nitrogen (N), and phosphorus (P), with consequences on soil microbial biomass stoichiometric characteristics. However, the temporal dynamics and coordination of soil-microbial C:N:P stoichiometry are still unclear. In this study, we examined the variations of soil-microbial biomass C, N, and P with the tea plantation ages (<5 a, 5-10 a, 10-20 a, 20-30 a, and >30 a) in a small watershed in the Three Gorges Reservoir Area. We analyzed the relationships between their stoichiometric ratios, microbial entropy ( q MBC, q MBN, q MBP), and stoichiometric imbalance (ratios of soil C, N, P stoichiometry to microbial biomass C, N, P stoichiometry). The results showed that with the increases of tea plantation ages, soil and microbial biomass C, N, P contents, soil C:N and C:P significantly increased, while soil N:P declined; the microbial biomass C:P and N:P increased first and then decreased, but microbial biomass C:N did not change. Tea plantation ages significantly affected soil microbial entropy and soil-microbial stoichiometry imbalance (C:N imb , C:P imb , N:P imb ). With the increases of tea plantation ages, q MBC first decreased and then increased, while q MBN and q MBP went up in a fluctuating pattern. The C-N stoichiometry imbalance (C:N imb ) and C-P stoichiometry imbalance (C:P imb ) increased significantly, while the N-P stoichiometry imbalance (N:P imb ) showed a fluctuating rise. Results of the redundancy analysis showed that q MBC was positively correlated with soil N:P and microbial biomass C:N:P, but negatively correlated with microbial stoichiometric imbalance and soil C:N, C:P; whereas q MBN and q MBP showed the opposite situation. The microbial biomass C:P was most closely related to q MBC, while C:N imb and C:P imb had greater effects on q MBN and q MBP.

Soil aggregates are the main sites for the decomposition of soil organic matter and the formation of humus. The composition characteristics of aggregates with different particle sizes are one of the indicators for soil fertility. We explored the effects of management intensity (frequency of fertilization and reclamation) on soil aggregates in moso bamboo forests, including mid-intensity management (T 1 , fertilization and reclamation every 4 years), high-intensity management (T 2 , fertilization and reclamation every 2 years), and extensive management (CK). The water-stable soil aggregates (0-10, 10-20, and 20-30 cm layers) from moso bamboo forest were separated by a combination of dry and wet sieving method and the distribution of soil organic carbon (SOC), total nitrogen (TN) and available phosphorus (AP) across different soil layers were determined. The results showed that management intensities had significant effects on soil aggregate composition and stability, and SOC, TN, AP distribution of moso bamboo forests. Compared with CK, T 1 and T 2 decreased the proportion and stability of macroaggregates in 0-10 cm soil layer, but increased that in 20-30 cm soil layer, while reduced the content of organic carbon in macroaggregates, the contents of organic carbon, TN and AP in microaggregates. Such results indicated that the intensified management was not conducive to formation of macroaggregates in 0-10 cm soil layer and carbon sequestration in macroaggregates. It was beneficial to the accumulation of organic carbon in soil aggregates and nitrogen and phosphorus in microaggregates with lower human disturbance. Mass fraction of macroaggregates and organic carbon content of macroaggregates was significantly positively correlated with aggregate stability, which best explained the variations of aggregate stability. Therefore, macroaggregates and organic carbon content of macroaggregates were the most important factors affecting the formation and stability of aggregates. Appropriate reduction of disturbance was beneficial to the accumulation of macroaggregates in the topsoil, the sequestration of organic carbon by macro-aggregates, and the sequestration of TN and AP by microaggregates, and improving soil quality and sustainable management in moso bamboo forest from the point of view of soil aggregate stability.

Litter-derived dissolved organic matter (DOM) is an important source of soil DOM, and the response of which to climate warming may change forest soil carbon and nitrogen dynamics, such as soil carbon and nitrogen mineralization. In this study, we conducted a field manipulative warming experiment in natural Castanopsis kawakamii forests. Combined with litter leaching solution collected in the field and ultraviolet-visible and three-dimensional fluorescence spectroscopy analyses, we explored the effects of warming on the content and structure of litter-derived DOM in subtropical evergreen broad-leaved forests. The results showed that litter-derived dissolved organic carbon and nitrogen content exhibited monthly dynamics, with the peak (in April) and the mean monthly content being 1.02 and 0.15 g·m -2 , respectively. Litter-derived DOM had higher fluorescence index and lower biological index, indicating the microbial-origin of DOM from litter. The litter DOM mainly included humic-like fractions and tryptophan-like substances. Warming did not affect the content, aromaticity, hydrophobicity, molecular weight, fluorescence index, biological index and humification index of DOM, suggesting neutral effect of warming on the quantity and structure of litter DOM. Warming also did not affect the relative contribution of main components in DOM, indicating that the temperature variation exerted no effects on microbial degradation. In summary, warming did not change the quantity and quality of litter-derived DOM in subtropical evergreen broadleaved forests, indicating warming had little effect on litter-derived DOM input to soil.

We examined the effects of fertile soil layer construction technology on soil fertility and maize yield with a 3-year field experiment in Albic soil in Fujin, Heilongjiang Province. There were five treatments, including conventional tillage (T15, without organic matter return) and fertile soil layer construction methods [deep tillage (0-35 cm) with straw return, T35+S; deep tillage with organic manure, T35+M; deep tillage with straw and organic manure return, T35+S+M; deep tillage with straw, organic manure return and chemical fertilizer, T35+S+M+F]. The results showed that: 1) compared with the T15 treatment, maize yield was significantly increased by 15.4%-50.9% under fertile layer construction treatments. 2) There was no significant difference of soil pH among all treatments in the first two years, but fertile soil layer construction treatments significantly increased soil pH of topsoil (0-15 cm soil layer) in the third year. The pH of subsoil (15-35 cm soil layer) significantly increased under T35+S+M+F, T35+S+M, and T35+M treatments, while no significant difference was observed for T35+S treatment, compared with T15 treatment. 3) The fertile soil layer construction treatments could improve the nutrient contents of the topsoil and subsoil layer, especially in the subsoil layer, with the contents of organic matter, total nitrogen, available phosphorus, alkali-hydrolyzed nitrogen and available potassium being increased by 3.2%-46.6%, 9.1%-51.8%, 17.5%-130.1%, 4.4%-62.8%, 22.2%-68.7% under the subsoil layer, respectively. The fertility richness indices were increased in the subsoil layer, and nutrient contents of the subsoil layer were close to those of topsoil layer, indicating that 0-35 cm fertile soil layer had been constructed. 4) Soil organic matter contents in the 0-35 cm layer were increased by 8.8%-23.2% and 13.2%-30.1% in the second and third years of fertile soil layer construction, respectively. Soil organic carbon storage was also gradually increased under fertile soil layer construction treatments. 5) The carbon conversion rate of organic matter was 9.3%-20.9% under T35+S treatment, and 10.6%-24.6% under T35+M, T35+S+M, and T35+S+M+F treatments. The carbon sequestration rate was 815.7-3066.4 kg·hm -2 ·a -1 in fertile soil layer construction treatments. The carbon sequestration rate of T35+S treatment increased with experimental periods, and soil carbon content under T35+M, T35+S+M and T35+S+M+F treatments reached saturation point in the experimental second year. Construction of fertile soil layers could improve the fertility of topsoil and subsoil and maize yield. In term of economic benefits, combination application of maize straw, organic material and chemical fertilizer within 0-35 cm soil, cooperating with conservation tillage, is recommended for the Albic soil fertility improvement.

Nitrogen (N) and silicon (Si) are important nutritional elements for rice. However, excessive N fertili-zer application and the ignorance of Si fertilizer are common in practice. Straw biochar is rich in Si, which can be used as a potential Si fertilizer. In this study, we conducted a consecutive 3-year field experiment to explore the effects of N fertilizer reduction combined with straw biochar application on rice yield, Si and N nutrition. There were five treatments: conventional N application (180 kg·hm -2 , N 100 ), 20% N reduction (N 80 ), 20% N reduction with 15 t·hm -2 biochar (N 80 +BC), 40% N reduction (N 60 ), and 40% N reduction with 15 t·hm -2 biochar (N 60 +BC). The results showed that compared with N 100 , 20% N reduction did not affect the accumulation of Si and N in rice; 40% N reduction reduced foliar N absorption, but significantly increased foliar Si concentration by 14.0%-18.8%; while combined application of biochar significantly increased foliar Si accumulation, with an increase of Si concentration by 38.0%-63.3% and Si absorption by 32.3%-49.9%, but further reduced foliar N concentration. There was a significant negative correlation between Si and N concentration in mature rice leaves, but no correlation between Si and N absorption. Compared with N 100 , N reduction or combined application of biochar did not affect soil ammonium N and nitrate N, but increased soil pH. Nitrogen reduction combined application of biochar significantly increased soil organic matter by 28.8%-41.9% and available Si content by 21.1%-26.9%, with a significant positive correlation between them. Compared with N 100 , 40% N reduction reduced rice yield and grain setting rate, while 20% N reduction and combined application of biochar did not influence rice yield and yield components. In summary, appropriate N reduction and combined with straw biochar can not only reduce N fertilizer input, but also improve soil fertility and Si supply, which is a promising fertilization method in double-cropping rice fields.

In recent years, the degradation of cropland soils in Northeast China, such as "thinned, barren, and hardened", has become increasingly serious, with consequences on sustainable development of agriculture. Based on the data from Soil Types of China (1980s) and Soil Series of China (2010s), we examined the change patterns of soil nutrient conditions across different regions and soil types in Northeast China over the past 30 years through the statistical analysis of large samples. The results showed that: 1) from the 1980s to the 2010s, soil nutrient indicators in Northeast China changed to different degrees. Soil pH decreased by 0.03. Soil organic matter (SOM) content decreasd most prominently, by 8.99 g·kg -1 or 23.6%. Soil total N (TN), total P (TP) and total K (TK) contents showed increasing trends, with increases of 17.1%, 46.8%, and 4.9%, respectively. 2) Changes in soil nutrient indicators differed across different provinces and cities. Soil acidification in Liaoning was the most obvious, with pH decreasing by 0.32. SOM content in Liaoning decreased most significantly, by 31.0%. Soil TN, TP, and TK contents in Liaoning increased most significantly by 73.8%, 248.1% and 44.0%, respectively. 3) The changes of soil nutrients varied greatly among soil types, with brown soil and kastanozems showing the greatest decrease in pH. The SOM content of all soil types showed a decreasing trend, with 35.4%, 33.8% and 26.0% reduction in brown soil, dark brown forest soil and chernozem respectively. The greatest increase in TN, TP and TK contents were observed in brown soil by 89.1%, 232.8%, and 48.5%, respectively. In summary, declining organic matter content and soil acidification were the core problems of soil degradation in Northeast China from the 1980s to the 2010s. Reasonable tillage methods and targeted conservation strategies are critically needed to ensure the sustai-nable development of agriculture in Northeast China.

Microbial biomass and community structure play a significant role in soil carbon cycling. There is a large amount of organic carbon in the subsoil, but most studies on soil microbial community have focused on the surface soil. The changes and influencing mechanisms of microbial community in subsoil are unclear. We analyzed soil microbial biomass and community structure at different soil depths (0-20, 20-40, 40-60, 60-80, and 80-100 cm) in three typical forests in southwest China, Xishuangbanna tropical rain forest, Ailao Mountain subtropical broad-leaved forest, and Lijiang temperate coniferous forest, by using phospholipid fatty acid technology, to explore their variation characteristics and influencing factors in different forests and soil depths. The results showed that contents of soil organic carbon and total nitrogen decreased gradually, microbial biomass declined significantly. The ratio of Gram-positive bacteria to Gram-negative bacteria (G + :G - ) reduced gradually, while the ratio of fungi to bacteria (F:B) increased with the increasing soil depth. Microbial community turned from G - -dominated which adapted to eutrophic environment into G + -dominated which adapted to oligotrophic environment. The three forest types differed little in soil microbial biomass, but different significantly in microbial community structure. Ailao Mountain subtropical broad-leaved forest and Lijiang temperate coniferous forest had much higher F:B at 0-20 cm than Xishuangbanna tropical rain forest, while significantly higher G + :G - at 0-100 cm in Xishuangbanna tropical rain forest was observed. Results of the redundancy analysis showed that the contents of soil organic carbon and total nitrogen were the main factors determining microbial biomass, with combined explanation of 78.3%. Results of the stepwise regression analysis showed that C:N was the most important driving factor on F:B and G + :G - . The change in microbial community structure and the decrease in biomass along soil profile might strongly affect the dynamics of soil organic carbon in southwest China forests.

To explore the stoichiometric characteristics of C, N and P and adaptive mechanism of mosses in mountain forest ecosystems, we set up 15 plots along the altitude gradient in Picea crassifolia forest in Helan Mountains, Ningxia. We analyzed the C:N:P stoichiometry of moss aboveground tissues and its relationship with environmental factors. The results showed the mean values of C, N and P concentration in moss aboveground tissues were 336.67, 20.31 and 0.66 mg·g -1 , respectively. The mean value of aboveground tissue N:P was 33.4, indicating that the growth of mosses was limited by P. The C concentration in the aboveground tissues of mosses was positively correlated with soil total nitrogen concentration and negatively correlated with soil total phosphorus concentration. The N concentration in aboveground tissues of mosses was significantly negatively correlated with soil organic carbon and soil total nitrogen concentrations. Results of redundancy analysis showed that the interpretation rate of environmental factors on the stoichiometry was 48.5%, with canopy closure, soil total nitrogen and soil total phosphorus as the main factors. Canopy closure was the main environmental factor affecting the growth of mosses in P. crassifolia forest in Helan Mountains. High canopy closure facilitated the growth of mosses.

Plants can alter soil microbial biomass and extracellular enzyme activities related with carbon (C), nitrogen (N), and phosphorus (P), through litter and root exudates, with consequences on soil carbon, nitrogen and phosphorus (P) cycling. However, it is not well known how the changes in soil phosphorus availability affect the relationships between plants and soil microorganisms. In this study, a factorial experiment was conducted to investigate the effects of Chinese fir ( Cunninghamia lanceolata ) planting and different levels of P addition (0, 1.95, 3.9, 7.8 and 15.6 g P·m -2 ·a -1 ) on soil microbial biomass and extracellular enzyme activities. The results showed that planting Chinese fir planting significantly altered soil microbial biomass and C- and N- and P-related extracellular enzyme activities, but the effects were dependent on P addition levels. Without P addition, Chinese fir planting significantly reduced soil nutrient availability and pH, which led to the aggravation of P limitation and lower soil microbial biomass. P addition relieved P limitation, and reduced soil acid phosphatase (ACP) activities by 30.0%, 30.5%, 35.3% and 47.1% with the increasing P addition level (1.95, 3.9, 7.8 and 15.6 g P·m -2 ·a -1 ). Under three P addition levels (1.95, 3.9 and 7.8 g P·m -2 ·a -1 ), the negative effects of Chinese fir planting on soil microbial growth were alleviated. Under the high P addition level (15.6 g P·m -2 ·a -1 ), the negative effects of Chinese fir planting on soil microbial growth occurred again due to soil N limitation. Taken together, Chinese fir planting and soil P availability generally affected soil microbial biomass and extracellular enzyme activities, and changed P limitation.

Tea plantations are an important N 2 O source. Fertilizer-induced N 2 O emission factors of tea plantations are much higher than other upland agricultural ecosystems. According to the basic information on characteristics and knowledge of N 2 O emissions from tea plantations around the world, we comprehensively reviewed N 2 O emission characteristics, production process, influencing factors, and reduction measures from tea plantations. The global means of ambient N 2 O emission and N 2 O emission stimulated by nitrogen fertilizer application from tea plantations were (2.68±2.92) kg N·hm -2 and (11.29±9.45) kg N·hm -2 , respectively. The fertilizer-induced N 2 O emission factor in tea plantations (2.2%±2.1%) was much higher than the IPCC-estimated N 2 O emission factor for agricultural land (1%). N 2 O emission from tea plantation soil (a typical acid soil) were mainly produced during nitrification and denitrification, with denitrification being dominant. N 2 O emission from tea plantations were significantly related to the amount of fertilizer application. Other factors, such as fertilizer type, could also affect soil N 2 O emissions in tea plantations. The main reduction methods of N 2 O emission from tea plantations included optimizing the amount and type of fertilizer, amending biochar, and rationally using nitrification inhibitors. In future, we should strengthen in-situ observations of soil N 2 O emission from tea plantations at both temporal and spatial scales, combine lab incubation and field studies to elucidate the mechanisms underling tea plantation soil N 2 O emissions, and use a data-model fusion approach to reduce uncertainties in the estimation of global N 2 O emission. These would provide theoretical support and practical guidance for reasonable N 2 O emission reduction in tea plantations.

Soil dissolved organic carbon (DOC) is the most active part in forest soil carbon pool, the responses of which to climate warming has profound effects on forest carbon cycling. Based on a manipulative soil warming experiment in subtropical evergreen broad-leaved forests, we collected soil solutions in situ and used ultraviolet-visible, infrared and three-dimensional fluorescence spectroscopy analyses to explore the effects of soil warming (+4 ℃, 1 year) on soil DOC quantity and quality along the soil profile. The results showed that soil DOC flux remained constant along the soil profile. Soil DOC mainly included two humic-like fractions and one microbial metabolite. Warming significantly decreased soil DOC flux and the abundance of aromatic and hydrophobic components, and increased the amount of low molecular weight carbohydrates. Furthermore, soil warming increased the relative proportion of humic-like fractions in the surface soil layer (0-10 cm) and microbial metabolite in the deep soil layer (30-40 cm), indicating that warming might accelerate microbial turnover in the deep layer. Overall, soil warming not only decreased soil DOC content, but also simplified the composition of soil DOC in subtropical evergreen broad-leaved forests.

The stability and adaptability of the critical nitrogen concentration in drip-irrigated cotton fields in Southern Xinjiang were investigated by measuring the nitrogen uptake ( N uptake ), nitrogen nutrition index (NNI), and accumulated nitrogen deficit ( N and ). A two-year field study was conducted using five nitrogen levels (0, 75, 150, 300, and 450 kg·hm -2 ), with cotton cultivars 'Xinluzhong55' and 'Xinluzhong78' as the test materials. We analyzed the effects of nitrogen addition on plant dry matter (PDM) and critical nitrogen concentration dilution curves (PNC c ). The N uptake , NNI, and N and models as well as a model of the relationships between NNI, N and, and the relative seed cotton yield (RY) were established based on the PNC c for both cultivars. The results showed that the PNC c , maximum nitrogen concentration (PNC max ), and minimum nitrogen concentration (PNC min ) dilution models in drip-irrigated cotton showed power function relationships with plant dry matter (PDM), with determination coefficients ( R 2 ) of 0.905 and 0.960, 0.919 and 0.950, 0.934 and 0.969 for Xinluzhong55 and Xinluzhong78, respectively. Model validation with independent experimental data showed that the critical nitrogen concentrations in cotton grown under drip-irrigated conditions were simulated satisfactorily. The Xinluzhong55 and Xinluzhong78 1:1 line R 2 , root mean square error (RMSE) and relative estimation error (RE) of the simulated and observed critical nitrogen concentrations were 0.987, 0.051 g·kg -1 , 1.95% and 0.984, 0.044 g·kg -1 , 1.91%, respectively, showing good stability and adaptability between the two years. According to the N uptake , NNI, and N and model, we concluded that 300 kg·hm -2 was the optimum level of nitrogen application in drip-irrigated cotton in Southern Xinjiang. Based on the fitting results of nitrogen level and seed cotton yield, the theoretical appropriate nitrogen applications for Xinluzhong55 and Xinluzhong78 were 322.7 and 336.4 kg·hm -2 , respectively. The R 2 of NNI, N and and RY in different growth stages were greater than 0.900, the NNI, N and and RY estimation model of seed cotton yield based on 1:1 lines of R 2 , RMSE, and RE were 0.899-0.989, 0.05-0.13, and 4.1%-9.9% and 0.902-0.981, 0.04-0.12, and 5.1%-9.5%, all of which were highly significant. These results could provide new directions for the evaluation and diagnosis of optimum nitrogen application levels and nitrogen status, as well as the estimation of seed cotton yield in drip-irrigated cotton in Southern Xinjiang.

Natural sod culture in orchard is an effective measure to improve the orchard productivity and promote the sustainable production. To explore the effects of inter-row grass ploughing and returning on soil biological cha-racteristics and nutrient contents, we examined the effects of different grass returning to the field on the amount of soil microorganisms, enzyme activities and nitrogen and potassium contents of 0-20 cm soil layer. There are three treatments, cleaning tillage as the control (CK), conventional mowing management (NG), and soil ploughing annually under natural sod culture with conventional mowing condition (NGR) treatments. The results showed that soil microorganisms were dominated by bacteria, followed by actinomycetes, with the least fungi. Compared with CK, both NG and NGR treatments significantly improved the abundance of soil bacteria and fungi, with the strongest effects in NGR treatment, and significantly increased the soil urease, sucrase and catalase activities by 59.0%, 20.7%, 38.3% and 73.5%, 45.9%, 67.8%, respectively. NGR treatment significantly increased soil nitrogen and potassium contents, with the contents of ammonium nitrogen, nitrate nitrogen, particulate organic nitrogen, microbial biomass nitrogen, available potassium and water-soluble potassium being 1.5, 1.8, 1.6, 2.0, 1.3 and 1.4 times of that in CK, respectively. NGR significantly increased soluble sugar content and sugar acid ratio and subsequently improved fruit quality. Overall, NGR increased soil microbial abundance, enzyme activities, nitrogen, potassium contents and fruit quality, which could be a feasible management of inter-row grasses in the natural sod culture apple orchard.

We explored the impacts of nitrogen (N) inputs and the rhizosphere effect on the properties of rhizosphere and bulk soils in a salinized grassland in Northern Shanxi under N addition rates of 0, 1, 2, 4, 8, 16, 24 and 32 g N·m -2 ·a -1 . The results showed that N addition significantly decreased soil pH, but significantly increased Ca 2+ , NO 3 - -N and inorganic nitrogen contents in rhizosphere and bulk soil. With the increases of N addition rates, the contents of Ca 2+ , NO 3 - -N, inorganic nitrogen in rhizosphere and bulk soils and total nitrogen in rhizosphere soil increased gradually, whereas the contents of Na + , K + , Mg 2+ , NH 4 + -N and amino acid in rhizosphere soil, and total nitrogen in bulk soil first increased and then decreased. Results of the principal component analysis showed that the responses of soil properties to low (≤8 g·m -2 ·a -1 ) and high nitrogen addition rates (>8 g·m -2 ·a -1 ) were significantly different. Compared with bulk soil, soil pH, the contents of organic acids and amino acids in rhizosphere soil were significantly lower by 0.71 units, 44.3% and 9.8%, respectively, while the contents of K + , Ca 2+ , Mg 2+ , NH 4 + -N, inorganic nitrogen, total carbon and total nitrogen in rhizosphere soil were significantly higher by 51.0%, 47.6%, 20.8%, 215.5%, 139.3%, 31.7% and 65.3%, respectively. These results indicated that rhizosphere effect on soil properties was stronger than that of nitrogen addition.

To explore the appropriate amount of phosphorus (P) fertilizer and improve economic yield and P use efficiency of edible sweetpotato, we took Xushu 32 as an example and compared the effects of different P application rates on yield, quality, P accumulation and P use efficiency of edible sweetpotato based on a two-year field experiment (soil available P content was 31.70 mg·kg -1 ) from 2018 to 2019. There were five P application levels (P 2 O 5 ), including 0 (P 0 ), 25 (P 25 ), 50 (P 50 ), 75 (P 75 ) and 100 kg·hm -2 (P 100 ). The results showed that, 1) compared with P 0 , P application significantly increased the yield of fresh sweetpotao and commodity potato, with the effects being the stongest under P 75 treatment, followed by P 50 treatment. However, there was no significant difference between the two treatments. 2) P application significantly increased the contents of starch and reducing sugar in storage root. The contents of soluble sugar and protein increased significantly under P 50 treatment. 3) Du-ring the growth period of 90 to 120 d, P fertilizer supply significantly increased P accumulation and dry matter accumulation of sweetpotato. 4) The apparent P use efficiency (APUE) decreased with increasing P application rates, while P agronomic efficiency (PAE) increased first and then decreased with the increases of P application rates, which was significantly higher under P 50 than other treatments. Taking into account the yield, quality, economic yield and P utilization rate of edible sweetpotato, the optimal dosage of P 2 O 5 is 50 kg·hm -2 under the experimental conditions.

By combining the composting process with soil culture experiment, we conducted an experiment with four treatments, including conventional chemical fertilizer (CK), chemical fertilizer + compost maturity reaching 50% germination index (GI, the same below) organic fertilizer (CO1), chemical fertilizer + compost maturity reaching 80% GI organic fertilizer (CO2), chemical fertilizer + compost maturity reaching 100% GI organic ferti-lizer (CO3). We measured soil microbial biomass nitrogen (MBN), mineral nitrogen (NH 4 + -N, NO 3 - -N), net nitrification rate, microbial biomass carbon (MBC), dissolved organic carbon (DOC), soil urease and soil protease, aiming to reveal the regulatory effect of soil MBN on mineral nitrogen. The results showed that organic fertilizer application significantly increased MBN and NH 4 + -N concentrations by 50.1%-62.4% and 109.9%-147.1%, reduced NO 3 - -N concentration and net nitrification rate by 23.3%-46.8%, and 26.2%-51.5%, and enhanced MBC, DOC, urease and protease activities by 33.8%-69.6%, 7.4%-20.8%, 11.2%-69.0% and 9.4%-25.1%, respectively. The change ranges of CO2 and CO3 were significantly higher than CO1. Redundancy analysis (RDA) and structural equation model (SEM) results showed that the application of organic fertilizer with higher degree of maturity (GI≥80%) positively regulated soil MBC, MBN, NH 4 + -N, and the activities of urease and protease, but had a negative effect on soil net nitrification rate. The combined application of chemical fertilizers and high decomposed organic fertilizers could significantly increase soil MBN and NH 4 + -N contents, as well as soil urease and protease activities, but reduce soil net nitrification rate. To efficiently utilize organic solid wastes, it is recommended to use chemical fertilizer in combination of organic fertilizers with 80% decomposing degree in practical production to reduce the cost in both economy and time.

Soil microorganisms play an important role in the biogeochemical cycles of terrestrial ecosystems. How-ever, it is still unclear how the amount and duration of nitrogen (N) addition affect soil microbial community structure and whether there is a correlation between the changes in microbial community structure and their nutrient limi-tation status. In this study, we conducted an N addition experiment in a subtropical Pinus taiwanensis forest to simulate N deposition with three treatments: control (CK, 0 kg N·hm -2 ·a -1 ), low N (LN, 40 kg N·hm -2 ·a -1 ), and high N (HN, 80 kg N·hm -2 ·a -1 ). Basic soil physicochemical properties, phospholipid fatty acids content, and carbon (C), N and phosphorus (P) acquisition enzyme activities were measured after one and three years of N addition. The relative nutrient limitation status of soil microorganisms was analyzed using ecological enzyme stoichiometry. The results showed that one-year N addition did not affect soil microbial community structure. Three-year LN treatment significantly increased the contents of Gram-positive bacteria (G + ), Gram-negative bacteria (G - ), actinomycetes (ACT), and total phospholipid fatty acids (TPLFA), whereas three-year HN treatment did not significantly affect soil microbial community, indicating that bacteria and ACT might be more sensitive to N addition. Nitrogen addition exacerbated soil C and P limitation. Phosphorus limitation was the optimal explanatory factor for the changes in soil microbial community structure. It suggested that P limitation induced by N addition might be more beneficial for the growth of certain oligotrophic bacteria ( e.g . G + ) and the microorganisms participating in the P cycling ( e.g . ACT), with consequences on soil microbial community structure of subtropical Pinus taiwanensis forest.

Planting grasses in orchards is important to maintain soil basic fertility, improve the soil ecological environment, and promote sustainable growth of fruit. However, the quantitative effects of grasses on nutrient content of orchard soil in China is unclear, as well as the mechanisms associated with higher fruit yield and quality in orchards. This meta-analysis included 62 literature published between 1990 and 2020 to quantify effects of soil depth, planting years of raw grasses, and raw grasses to the physical and chemical properties and fruit yield and quality of orchards, as well as to explore the impacts of grasses on the sustainable production of Chinese orchards. Between 1990 and 2020, compared with the non-grass orchards, the content of soil organic matter, alkali nitrogen and available phosphorus in orchard with grasses increased by 18%, 11%, and 27% respectively, and the soil bulk density was reduced by 20%. Orchard grass increased soil temperature by 23% when the temperature was below 10 ℃, and reduced soil temperature by about 8% when the temperature was above 10 ℃. Compared with annual grasses, perennial grasses (natural or artificial) significantly improved soil properties, fruit yield and quality. These findings indicated that long-term grass planting in orchards had far-reaching significance on sustainable production.

This study amined to explore the variation of soil organic nitrogen components across the degradation succession of Gahai Wetland. By combining field sampling and laboratory analysis, the content and distribution characteristics of soil organic nitrogen components, i.e., hydrolytic total nitrogen (HTN), unidentified acidolytic nitrogen (HUN), ammonium nitrogen (AMN), amino acid nitrogen (AAN) and acid amino sugar nitrogen (ASN) were investigated in undegraded (UD), lightly degraded (LD), moderately degraded (MD), and heavy degraded (HD) Gahai Wetland. The results showed that, in the 0-10 cm layer, the contents of total nitrogen (TN), HUN, AMN, and AAN in LD decreased by 17.3%, 19.4%, 8.6%, and -5.6%, 28.0%, 19.4%, 17.1% and 0 in MD, and 35.8%, 28.8%, 28.6% and 55.6% in HD, respectively. In the 10-20 cm layer, the four components decreased by 4.0%, 10.3%, 2.9% and 9.1% in LD, 21.0%, 18.3%, -2.9% and -9.1% in MD, and 9.9%, 38.9%, 21.2% and 51.4% in HD, respectively. The corresponding contents in the 20-40 cm soil layer did not change. The proportion of soil acid-hydrolyzed nitrogen components to TN under four degradation stages was HUN (25.9%-32.5%) &gt; AMN (6.7%-11.1%) &gt; AAN (4.8%-11.1%) &gt; ASN (1.2%-4.4%). Soil water content was the main driving factor for variations of soil organic nitrogen components as indicated by the results of redundancy analysis. Degradation of the Gahai Wetland significantly reduced the content of soil TN and the components of acid-hydrolyzed nitrogen in 0-10 cm soil layer, and weakened the nitrogen "sink" function of soils. The AAN and ASN were sensitive to wetland degradation.

Excessive nitrogen application would deteriorate soil structure and increase greenhouse gas emission. We set up six treatments, i.e., N 0 , N 120 , N 180 , N 240 , N 300 and N 360 (nitrogen application rates of 0, 120, 180, 240, 300 and 360 kg·hm -2 , all straws returned into the field in situ) in the nitrogen fertilizer experimental site to investigate the effects of different nitrogen application rates on soil N 2 O emission, soil water-filled porosity (WFPS), soil temperature, nitrate and ammonium contents, composition and stability of water stable aggregates in winter wheat filed in 2018-2020. The results showed that there was a significant positive correlation between soil N 2 O emission and nitrogen application rate. There was no correlation between WFPS and nitrogen application rate. Soil temperature in the 0-10 cm layer decreased significantly with the increases of nitrogen application rates. There was a significant positive correlation between nitrate and ammonium contents and nitrogen application rate. With the increases of nitrogen application rates, the content of water stable aggregates with diameter &gt;2 mm decreased, while that of water-stable aggregates with diameter &lt;0.5 mm increased. The particle size of soil water-stable aggregates also decreased gradually. There was a significant negative correlation between nitrogen application rate with mean weight diameter (MWD) and geometric mean diameter, while no correlation with fractal dimension. The fitting equation between MWD and N 2 O emission flux was y=3928.3e -2.171x (R 2 =0.55, P&lt;0.001), indicating that N 2 O emission increased markedly as MWD decreasing. The increases in nitrogen application rate reduced soil temperature in the 0-10 cm layer, increased nitrate and ammonium contents, decreased the average particle size of soil water stable aggregates, and the stability of soil aggregates, and increased soil N 2 O emission.

We explored the responses of the quantity and quality of soil dissolved organic matter (DOM) to short-term nitrogen (N) addition across an addition gradient (0, 40, and 80 kg N·hm -2 ·a -1 ) and their correlation with bacterial communities in Pinus taiwanensis forest in the Daiyunshan Nature Reserve, Fujian, China. Soil DOM and bacterial community composition were measured using three-dimensional fluorescence and parallel factor analyses combined with high-throughput sequencing. The results showed that compared with the control, N-addition reduced the content of dissolved organic carbon (DOC) and the humification index (HIX) of DOM in the 0-10 and 10-20 cm soil layers, with significant reduction under the high N addition (80 kg N·hm -2 ·a -1 ). Results of parallel factor analysis further showed that the relative content of humus-like components (C1, C2) in DOM decreased following N addition. Short-term N addition reduced the relative abundance of copiotrophic bacteria (Proteobacteria and Acidimicrobiia), but increased the relative abundance of oligotrophic bacteria (Spartobacteria). The relative abundance of copiotrophic bacteria were positively correlated with the HIX and refractory humus-like components (C1, C2) and negatively correlated with the relatively easily decomposed fulvic acid-like component (C3), whereas the pattern was opposite for oligotrophic bacteria. It is indicated that bacterial communities with different life strategies had obvious preference for difficult- and easy-to-decompose components in DOM under N addition treatments. We speculated that the transformation of soil microbial life strategies under the background of increasing N deposition might alter DOM components.

Unscientific fertilization, unstable grain quality, and low profit are the key problems on wheat production in slope cropland of Western Hubei. To solve these problems, three optimized planting patterns (high nitrogen and potassium reduction, HNPR; medium nitrogen and potassium reductionm, MNPR; low nitrogen and potassium reduction, LNPR) were conducted during two consecutive years to assess their effects on wheat yield, quality, profit, and fertilizer use efficiency in Danjiangkou Reservoir area, a typical slope cropland region with wheat-maize rotation. The results showed that the application of chemical fertilizer significantly increased grain yield (GY) and wet gluten content (WGC) of wheat. Compared with the conventional planting pattern (CK), the partial factor productivity (PFP K ) and agricultural fertilizer use efficiency (AFUE K ) of potassium were significantly improved in the three optimized planting patterns. The dry matter amount (DMA), GY, and crude protein content (CPC) were the highest under HNPR, which increased by 9.4%, 19.4%, and 7.8% than CK, respectively. Such a result indicated that HNPR benefited wheat to exploit high yield potential. WGC and falling number (FN) were the highest under MNPR, and increased by 3.9%, and 9.3% than CK, respectively, which was suitable for high-efficiency production of medium-gluten wheat. PFP N , AFUE N , PFP K , AFUE K , and net profit were the highest under LNPR, which increased by 15.7%, 134.1%, 131.3%, 368.2%, and 37.3% than CK, respectively, while the CPC and WGC were decreased by 2.1% and 2.6% than CK, respectively, suggesting it was suitable for environment-friendly and simplified production of weak-gluten wheat production. Our results could provide a reference for wheat production in the slope cropland.

We examined the effects of nitrification inhibitors (NIs) on soil nitrification, maize yield and nitrogen use efficiency (NUE), aiming to screen out high efficiency stabilized ammonium chloride fertilizer in red soil. Nitrification inhibitors 2-chloro-6-trimethyl-pyridine (CP), 3, 4-dimethyl-pyrazolate phosphate (DMPP), and dicyandiamide (DCD) and their combinations were added into ammonium chloride (NH 4 Cl) to make six stabilized nitrogen fertilizers. With blank (CK) and NH 4 Cl (N) as the controls, we conducted a maize pot experiment with the same amount of nitrogen addition. The results showed that compared with the treatment of N, soil ammonium content in CP+DMPP and DMPP+DCD increased by 56%-62%, which was significantly higher than that in CP, DMPP, and DCD, while the apparent nitrification rate of red soil was significantly reduced by 33%-34%. All the six treatments with nitrification inhibitors and their combinations significantly improved biomass and nitrogen absorption efficiency of maize. Compared with the N treatment, the application of adding NIs alone was significantly higher than that of the treatments of NIs combinations, with an average of 1.3 times increase. DCD was the most efficient one in improving maize yield, nitrogen uptake, and nitrogen adsorption efficiency, which increased by 4.1, 6.3 and 4.4 times, respectively. Comprehensively, DCD performed the best in reducing cost and improving yield and nitrogen use efficiency in red soil.