Search

• Wetlands topsoil can sequester more C than farmlands and forestlands. • Soil water content was important factor affecting microbial abundance and enzyme activity. • Higher soil water content can increase soil C storage by stimulating C fixing enzyme activity. • Soil C storage were negatively driven by soil bacterial abundance under different land-use. Soil carbon storage plays a crucial role in mitigating the climate warming and is significantly impacted by the land use pattern. To better understand soil carbon stability and the underlying microbial mechanism, based on qPCR, ELISA, and fluorescence techniques, the effects of land use changes on soil microbial abundance, enzyme activity, and soil carbon storage were investigated in the complex ecosystems of cropland, forestland, and wetland along three typical river (Wolvlan river, Bielahong river, Wusuli river) basin in Sanjiang Plain, China. We hypothesised that croplands soil carbon storage is lower than forestlands and wetlands, which is regulated by soil water content, microbe and enzyme activity. Results showed that topsoil TC in wetlands (85.54 mg·g−1) was higher than those in croplands (33.46 mg·g−1) and forestlands (46.13 mg·g−1). Topsoil water content increased 73.90 % and 71.64 % in wetlands than in farmland and forestlands, respectively. Additionally, reclamation diminished topsoil carbon storage. In croplands, soil dissolved organic carbon, microbial biomass carbon, microbial biomass nitrogen, available nitrogen, bacterial abundance, and soil enzymes (i.e., RubisCO, β-glucosidase, cellobiohydrolase, 1,4-N-acetylglucosaminidase and acid phosphatase) activities were substantially lower than those in wetlands. Structural equation modeling showed that soil carbon storage was positively related to soil water content and RubisCO activity but negatively related to soil bacterial abundance. Soil water content had the largest standardised total positive effect coefficient and indirectly influenced soil carbon storage by affecting RubisCO activity. Soil depth had a greater effect on SMC, hydrolase and site had a greater effect on bacteria and fungi abundance. The results highlight that the alteration of carbon fixing enzyme activity by soil water content is a crucial mechanism for soil carbon sequestration in response to land-use change. Management strategies that conserve natural wetlands, increase soil water content and minimize land disturbance would be effective in maintaining soil carbon stocks. [ABSTRACT FROM AUTHOR]

• Spatial variations in soil erodibility was quantified by indicators in karst hillslope. • Identify the predominant factors affecting spatial variations in soil erodibility. • Land use and slope position had great effects on near-surface soil characteristics. • CSEI varied with land use and slope position, and affected by soil characteristics. Land use type and slope position have a considerable impact on soil properties and thus likely influence soil erodibility. Soil erosion on karst hillslopes in South China is still serious due to the high intensity of human activities and fragile ecological environment. Nevertheless, the potential effects of land use type and slope position on soil erodibility indicators in karst areas are still unclear. This study was conducted to investigate the spatial variations in soil erodibility indicators, namely, the saturated hydraulic conductivity (K S), mean weight diameter (MWD), soil structural stability (SSI), soil erodibility K factor, soil organic carbon content (SOC), and a comprehensive soil erodibility index (CSEI) for three typical land uses and three slope positions on a karst hillslope. The results showed that K S , MWD , SSI , K factor, SOC and CSEI varied significantly with land use type and slope position. The measured K S , MWD , SSI , K factor and SOC at the nine tested sites displayed a similar trend with soil depth. SOC , MWD and SSI contributed more to the CSEI , with contributions of 27.9%, 25.9% and 25.9%, respectively. K S and K factor contributed less to the CSEI , with contributions of 17.7% and 2.5%, respectively. Woodland is most susceptible to erosion on upper, cropland on middle and grassland on lower slope positions according to the values of CSEI. There were significant positive correlations among sand content, bulk density and CSEI , and there were significant negative correlations among clay content, silt content, root mass density, SOC and CSEI. The changes in soil properties and soil erodibility indicators with land use type and slope position led to the differences in the CSEI. The results provide valuable information for policymakers to select appropriate land use types to mitigate soil erosion and thus improve the healthy development of the ecological environment on karst slopes. Moreover, the results have crucial implications for understanding the mechanism of the spatial variation in soil erosion of karst hillslopes in Southwest China. [ABSTRACT FROM AUTHOR]

• The mean soil organic carbon (SOC) content in agroecosystem of Eastern China was 18.24 g kg−1. • The SOC content of planted forest > cropland > grassland in the total study area. • The SOC value of grassland was higher than cropland in North China due to excessive mechanized operation. • The random forest hybrid model exhibited higher comprehensive performance in SOC prediction. • Our predictions were much more detailed and accurate than the existing SOC content maps. Soil organic carbon (SOC) plays a key role in soil function, ecosystem services, and the global carbon cycle. Large SOC stocks accumulate in agroecosystems, but the estimates of SOC distribution and magnitude in agroecosystems still have large uncertainties in global products. Based on multiple high-resolution environmental variables (terrain derived from digital elevation model, climate and organism from Landsat 8 OLI) and 369 observed soil samples from 2019 to 2021, two machine learning methods, random forest (RF) and support vector machine (SVM) models, were used to estimate the content and spatial distribution of SOC in agroecosystems of Eastern China. We proposed a hybrid model in which the optimal predictors of SOC were selected for different land use types (cropland, planted forest and grassland), and it aimed to improve the performance of machine learning. Our results showed that (1) the hybrid models performed better than the global models, and the Random forest-Hybrid (RF-Hybrid) model led to the highest prediction accuracy, with a validation R2 of 0.65 and RMSE of 5.76 g kg−1. (2) The SOC content in the agroecosystems of Eastern China among different land use types ranked in the following order: planted forest (19.92 g kg−1) > cropland (17.51 g kg−1) > grassland (17.30 g kg−1). However, in North China, the SOC content in cropland (14.04 g kg−1) was much lower than that in planted forest (17.21 g kg−1) and grassland (17.07 g kg−1), which was caused by excessive mechanized operation. (3) The agroecosystem in Northeast China presented the highest mean SOC content (26.55 g kg−1) due to low temperature. (4) Our estimations (R2 = 0.53, RMSE = 6.74 g kg−1, 30-m resolution) were more detailed and precise than the existing global SOC maps (Soil Grids: R2 = 0.26, RMSE = 12.44 g kg−1, 250-m resolution; HWSD: R2 = 0.06, RMSE = 41.07 g kg−1, 1000-m resolution). The results may improve the accuracy of agroecosystem carbon mapping and contribute to SOC assessments in agricultural ecosystems. [ABSTRACT FROM AUTHOR]

• Facility lands were considered to be greater carbon sinks compared to other land uses. • The most stable type of organic carbon is in facility land, and the most unstable is in grasslands. • Changes in land use have a significant impact on organic carbon fractions and carbon mineralization. Soil carbon is an essential component that influences soil health and agronomic productivity, and land-use practices significantly impact soil carbon stocks. In this study, the researchers investigated the impact of various land-use types (farmland, orchards, grasslands, and facility lands) on soil organic carbon (SOC) fractions in the Qaidam Basin of China's Qinghai-Tibet Plateau. The soil samples were taken from the 0–10 and 10–20 cm depths. The particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) fractions of various land uses have been measured. The results revealed that grasslands had the greatest POC/SOC ratio (0.59), with POC accounting for the majority of the SOC fraction. In contrast, all other land-use types (facility land, orchards, and farmland) had greater MAOC/SOC ratios than POC/SOC. The facility land had the highest SOC content (17.75 g kg−1), and orchard had the lowest (8.51 g kg−1). The grassland had the highest POC content (9.82 g kg−1) at a depth of 0–10 cm. The trend for MAOC content among the various land-use types was facility lands > farmlands > grasslands > orchards. The soil pH was also observed to be moderately alkaline, with an average of 8. The orchard has the highest bulk density (BD), measuring 1.38 g cm−3. The grasslands contained the highest amount of total nitrogen (TN) (2.2 g kg−1) while the agricultural fields contained the highest amount of total phosphorus (TP) (1.16 g kg−1). In addition, facility lands showed the highest level of microbial activity compared to other land-use types. According to the findings, SOC, POC, and MAOC fractions had considerably positive associations with TN and microbial biomass carbon (MBC), but were significantly negatively associated with metabolic CO 2. The findings imply that different land-use types can have a considerable impact on the quality and amount of soil organic carbon, which has consequences for soil health and ecosystem processes. The findings also highlight the significance of long-term land management practices that promote the preservation and enhancement of soil organic carbon in various land-use systems. [ABSTRACT FROM AUTHOR]

Composition and stability of soil organic matter (SOM) affect the sustenance and productivity of soil over the long-term. This issue is particularly important for karst regions in China where the water supply and fertilizer use are limiting factors. Here, we used four indicators to evaluate changes in the composition and stability of SOM quantitatively in five main land-use types in karst area, including primary forest [PF], 15-year secondary forest [SF], grazing secondary forest [GF], abandoned farmland [AF] and farmland [FL]. We collected soil samples at a depth of 0–20 cm to conduct the analyses. Four indicators were used: soil physical and chemical properties, active organic carbon (C), humus C composition, and SOM functional groups. Our results showed that the content of SOM, total nitrogen, and easily oxidized organic C at 0–20 cm soil depth differed among the five land-use types ( P < 0.05). For humic acid C concentration, the land-use types were ordered as: SF > PF > GF > FL > AF. Solid-state 13 C NMR spectra showed that the highest ratio of Alkyl C/O-alkyl C was in AF, while the lowest was in SF. Overall, the comprehensive quality of SOM in different land-use types was PF (setting 100%) > SF (83.1%) > GF (58%) > AF (30.9%) > FL (29.9%). For karst areas, we suggest that farmlands in sloping area should be converted back to forests, with only moderate grazing being permitted, whereas farmlands in the plains should implement grain-forage rotation and grain-soybean rotation to meet the needs of the growing population and economic development. In conclusion, our findings provide a scientific basis from which to delineate rational land-use types for different land (geographical and geological) formations. [ABSTRACT FROM AUTHOR]

The impact of land use on the content of labile soil organic carbon (SOC) has been studied well. However, limited information is known about its effect on the recalcitrant SOC pool, which is a key proxy for long-term carbon sequestration. We investigated the impact of land use change on the distribution of labile and recalcitrant SOC fractions in soil profiles (0–30 cm) in the Jinchuan peatland, Northeast China, where native peatland (with peat soil) and forest (with mineral soil) are converted to paddy and cropland, respectively. Peat and mineral soil profile samples were collected from 10 sites in native and cultivated land. Total organic carbon (TOC) and KMnO 4 -oxidizable carbon (KOC) defined as the labile SOC fraction were measured in both peat and mineral soils. Fibre and lignin were also determined in peat samples. The mineral-associated organic carbon (MOC) and black carbon were examined as two recalcitrant SOC fractions. In peat soil profiles, the TOC and KOC contents increased with the increasing depth across all land uses. The conversion of peatland to paddy field can affect TOC content at each peat soil depth. The KOC content was lower in cultivated soils, indicating that cultivation decreased KOC. The KOC decrease was smaller than the TOC decrease, indicating that some recalcitrant SOC fractions were decomposed because of land use change. Unlike peat soil profiles, the TOC and KOC contents decreased with depth in mineral soil profiles across all land uses. The TOC and KOC contents in surface soil decreased remarkably after cultivation to cropland but were not affected in deep soil. Interestingly, recalcitrant SOC fractions, such as MOC, increased in mineral soil profile after cultivation but showed no change in peat soil profile. This study suggests that conversion of peatland to paddy can release the recalcitrant SOC fraction. In addition, conversion of cultivated forest to cropland decreased the TOC content but prolonged the long-term storage of some recalcitrant SOC fractions, such as MOC. [ABSTRACT FROM AUTHOR]

We examined the impact of human changes in land use on the concentrations and stoichiometric relationships among soil carbon (C), nitrogen (N), phosphorus (P) and potassium (K) in a Phragmites australis riparian wetland (Minjiang River estuary, China). We compared a natural (unaltered) wetland with five altered land uses: intertidal mudflat culture and vegetable, flower, fruit and rice cultivations. All these land uses decreased C, N and K soil concentrations relative to those in the P. australis wetland. The close relationship between total soil C and N concentrations, under all land uses, suggested that N was the most limiting nutrient in these wetlands. The lower N concentrations, despite the use of N fertilizers, indicated the difficulty of avoiding N limitation in the agricultural land. Croplands, except rice cultivation, had lower soil N:P ratios than the original P. australis wetland, consistent with the tendency of favoring species adapted to high rates of growth (low N:P ratio). The release of soil C was less and the soil C:N and C:P ratios higher in the natural P. australis riparian wetland than in the croplands, whereas C storage was more similar. The levels of soil C storage were generally opposite to those of C release, indicating that C release by respiration was the most important factor controlling C storage. Cropland soil management promotes faster nutrient and C cycles and changes in soil nutrient stoichiometry. These impacts can further hinder the regeneration of natural vegetation by nutrient imbalances and increase C-cycling and C emissions. [ABSTRACT FROM AUTHOR]

• Driving factors of SOC and total N were explored in 28 lucerne fields. • The SOC and total N were mainly explained by soil resources. • Soil P, moisture, and altitude were the key factors affecting SOC and total N. • Plant species diversity positively affected SOC and total N contents. • A strong interaction effect was observed among topography, vegetation and soil on SOC. Lucerne (Medicago sativa L.) is one of the most successfully introduced species for revegetation on the Loess Plateau of China and provides important ecosystem services. However, the driving mechanism of soil organic carbon (SOC) and total nitrogen (TN) in lucerne grasslands remains unclear. This study explored the controlling factors of SOC and TN in lucerne grasslands in the semiarid Loess Plateau. A total of 112 quadrats were employed in 28 lucerne fields. Vegetation characteristics, topographic factors, and soil properties at a 0–20 cm depth were measured in each quadrat. The SOC and TN contents increased with altitude and showed positive correlations with species richness, aboveground biomass of native plants, soil moisture, soil inorganic nitrogen, total soil phosphorus (P), and C:P and N:P ratios. Variations in SOC and TN contents were mainly attributed to soil resources, followed by the interaction of topography, vegetation and soil. Soil P, soil moisture, altitude, and native plant species were the main factors controlling SOC and TN contents in these lucerne grasslands. Results suggest that specific abiotic (soil P and moisture) and biotic (plant species diversity) factors controlled SOC and TN in semiarid lucerne grasslands. These factors should be included in SOC and TN evaluation models to predict the future terrestrial ecosystem carbon and nitrogen dynamics. [ABSTRACT FROM AUTHOR]

[Display omitted] • The interactive effects of soil erosion and land use on SOC were studied. • Soil erosion rates were higher in orchard land relative to farmland. • The direct impact of soil erosion accounts for 1.5% of SOC variability in soil surface. • The direct or indirect effects of land use accounts for 89.0% for SOC variability in deeper soil. Changes in land use can result in soil erosion and the loss of soil organic carbon (SOC). However, the individual contribution of different land use types on SOC variability as well as the combined impacts of land use and soil erosion are still unclear. The aims of the present study were to: (1) evaluate soil erosion and SOC contents under different land use types, (2) identify the influences of soil depth and land use on SOC content, and (3) determine the contribution of land use and soil erosion on SOC variability. We assessed the SOC and total soil nitrogen (TSN) contents under three types of land use in the dry-hot valley in southern China. Caesium-137 (137Cs) and excess lead-210 (210Pb ex) contents were also measured to determine soil-erosion rates. Land use was found to significantly affect soil erosion, and erosion rates were higher in orchard land (OL) relative to farmland (FL), which is in contrast with previous study results. SOC and TSN contents varied significantly between the three land use types, with highest values in forest land (FRL) and lowest values in OL. SOC was found to decrease with decreasing soil depth; the highest rate of reduction occurred in the reference site (RS), followed by FRL and FL. The interaction between soil erosion and land use significantly impacted SOC in the soil surface layer (0–12 cm); the direct impact of soil erosion accounted for 1.5% of the SOC variability, and the direct or indirect effects of land use accounted for the remainder of the variability. SOC content in deep soil was mainly affected by factors related to land uses (89.0%). This quantitative study furthers our understanding on the interactive mechanisms of land use and soil erosion on changes in soil organic carbon. [ABSTRACT FROM AUTHOR]

• The number of organic phosphate-solubilizing bacteria (PSB) increased with soil TP. • The number of phosphate-solubilizing fungi (PSF) increased with soil carbon content. • The ability to solubilize phosphate was organic PSB > PSF > inorganic PSB. • The organic PSB was the best bacterial group to solubilize phosphate. Some soil bacteria and fungi are known to solubilize phosphates and play an important role in supplying phosphorus (P) to plants. In this study, we characterized the phosphate-solubilizing bacteria and fungi as well as P availability in latosols from southern China under different land use practices. Three different latosols (i.e., red soil, lateritic red soil and laterite red soil), each with four different land uses (i.e., agricultural land, grass land, forest land and orchard land), from Guangdong Province, China, were chosen to determine the amounts of phosphate-solubilizing bacteria (PSB) and phosphate-solubilizing fungi (PSF) and their phosphate solubilizing abilities. Our results show that the amount of available P (AP) increased with the amount of PSB favored in solubilizing organic P (or PSBop), while the amount of PSF increased with the content of soil organic carbon (SOC). The average rates of phosphate solubilization were 28.23% for PSBop, 6.97% for PSF, and 0.16% for PSBip (PSB favored in solubilizing inorganic P). An increase in soil pH decreased the ability of PSB to solubilize phosphate in latosols. This ability occurred in the following order: PSBop > PSF > PSBip. No significant difference in the amount of PSF was observed among the four different land uses for the lateritic red soil and laterite red soil, whereas a profound significant difference was found for the red soil, with the highest number of PSF in the grass land. Reasonable linear correlations between the PSB and the AP and between the PSF and the SOC were obtained and could provide a good reference to characterize soil PSB and PSF. Additionally, PSBop was the best bacterial species to solubilize phosphate in the latosols. [ABSTRACT FROM AUTHOR]

• The increase rate of active C was higher than those of intermediate and passive C. • Increased proportion of active C with the forest age led SOC to become more labile. • The increase of C:N ratio verified that SOC becomes more labile after reforestation. Land use changes have a great impact on carbon (C) cycling of terrestrial ecosystems by changing both the C inputs and mineralization rates. It not only results in variations of SOC stocks, but that the SOC properties could also change after vegetation conversions. In this study, we collected soil samples in a series of forests converted from croplands at different times in Southeast China. The effects of the reforestation on SOC pools and stabilities were investigated based on information of SOC contents, SOC fractions (active, intermediate and passive C) and C:N ratios. The organic carbon (OC) contents of the bulk soil and soil fractions increased with the forest ages in both topsoils (0–10 cm) and subsoils (40–50 cm). The increase rates of the active C were higher than those of the intermediate and passive C. As a result, the proportion of the active C increased with the forest ages, which would result in an increase of SOC instabilities. This was confirmed by the observation that the C:N ratio of the bulk soil increased with the forest ages. Our results implied that the C sink potential of the forest soil is to a large extent determined by the forest age. [ABSTRACT FROM AUTHOR]

The natural abundance of δ15N in soils is a simple tool for understanding ecosystem nitrogen cycling. However, the main drivers for soil δ15N in different natural land use types are not clear enough. To investigate the main drivers for soil δ15N in different land uses, we measured δ15N in the top 10 cm of the soil along a precipitation gradient with various land uses on the Loess Plateau of China, which covers a total area of 620,000 km2 and is one of the most erodible area in the world, to determine effects of climatic, soil and vegetation factors on soil δ15N and the relationships between them using the partial least squares regression (PLSR) method. Soil δ15N ranged from 1‰ to 9‰ on the Loess Plateau with an average of 5.8‰ in forest lands, 5.6‰ in shrub lands, and 4.8‰ in grasslands. Calculated variable influence on projection by PLSR showed that both soil properties (including soil organic carbon content, total nitrogen content and soil texture) and mean annual precipitation influenced soil δ15N strongly. In addition, site elevation also influenced soil δ15N strongly in forest lands. The dominant controls of soil δ15N varied among three land use types on the Chinese Loess Plateau, and PLSR would be a reasonable tool to predict soil δ15N. • Soil δ15N was analyzed on the Loess Plateau and globally in different land uses. • Precipitation, soil C and N influenced soil δ15N strongly on the Loess Plateau. • Equations between soil δ15N and the main factors were built on the Loess Plateau. • Regional equations did not work on global scale due to large precipitation range. [ABSTRACT FROM AUTHOR]