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Forest ecosystems are essential to the global carbon cycle because they are the biggest terrestrial carbon reserves. In the management of forests, thinning is a commonly employed strategy, impacting the respiration and biomass loss of trees, thereby modifying forest carbon dynamics. However, there is a lack of scientific research to confirm the impacts of thinning intensities on carbon storage in trees, soil layers, shrubs, and ground vegetation layers as well as its impact on wood production and growth rate. The goal of this study was to find the optimal thinning levels for increasing carbon sequestration during the growth stage of the Korean pine (Pinus koraiensis) middle-aged plantations in Northeast China. In this study, thinning intensity (0, 10, 11, 16, 18, and 22%) affected the carbon storage of trees, tree growth, volume, and, we suspected, soil layer, shrubs, and vegetation (herbs, litter, and grass) also. Specifically, after four years of thinning, the 18% treatment significantly increased total carbon storage, individual organ storage, growth, and tree volume (p < 0.05). These results give us abundant information about how thinning affects the dynamics of carbon storage, wood production, and the interactions between soil and plants in P. koraiensis plantations, contributing to multi-objective management strategies for optimizing carbon sequestration, wood production, and ecosystem health. [ABSTRACT FROM AUTHOR]

Climate change mitigation and carbon neutrality are current hot topics. Forests, urban green spaces, and wetland ecosystems are recognized as important carbon sinks. The Yangtze River Delta region in Eastern China, which plays a pivotal role in China's economic and social development, is rich in such carbon-sink resources. There is, however, a lack of regional carbon data. The investigation of carbon storage and carbon densities of forest, urban green space, and wetland ecosystems is, therefore, of great importance. In this study, the forest resource management map (including wetland) and green space system planning map of Changzhou city, combined with a field investigation and laboratory experimental analysis, were used to estimate the carbon storages and carbon densities of the forest, urban green space, and wetland ecosystems in Changzhou city. The average carbon density and carbon storage in Changzhou were 83.34 ± 4.91 Mg C ha−1 and 11.30 ± 0.67 Tg C, respectively, of which soil accounted for 74%, plants accounted for 25%, and litter accounted for less than 1%. The forest ecosystem contributed the most to the carbon pool (72%), with the green space ecosystem and the wetland ecosystem each accounting for 14% of the carbon pools. Clearly, the forest, green space, and wetland ecosystems in Changzhou city have a large carbon storage capacity. This study is of significance as it provides data on the carbon sink functions of forest, green space, and wetland ecosystems at the provincial and national regional scales. [ABSTRACT FROM AUTHOR]

Question: Patchiness of herbaceous species is a common feature of degraded alpine grasslands on the Qinghai–Tibet Plateau; however, the impact of this phenomenon on vegetation, soil seed bank (SSB), and soil carbon (C) and nitrogen (N) is largely unknown. We asked how different herbaceous patches affect above‐ground vegetation, the SSB and soil organic C (SOC) and total N (TN) contents in alpine meadows. Location: An alpine meadow on the Qinghai–Tibetan Plateau, China. Methods: We used field and greenhouse experiments to evaluate above‐ground vegetation parameters, the SSB composition, and SOC and TN contents of four commonly distributed herbaceous patches (Leymus secalinus, Kobresia humilis, Leontopodium nanum and Pedicularis kansuensis) and non‐patch vegetation (control). Results: There were significant differences in the species composition of above‐ground vegetation, with the plant species richness, Shannon–Wiener index, Simpson index, and Pielou evenness index reduced in the four patches compared to the control. In addition, patches had increased above‐ground biomass (AGB) and a lower below‐ground biomass to above‐ground biomass ratio (BGB:AGB); while the species diversity indices did not change considerably among the patches. The species composition of the SSB in the four patches differed from that in the control and the seed density increased markedly, but the species richness and diversity of the SSB remained unaltered. Moreover, the contents of SOC, total C, TN, microbial biomass C, and microbial biomass N in the four patches were markedly lower than in the control. Conclusions: These findings suggest that patchiness of herbaceous species can alter the flora composition of alpine meadows and reduce plant species diversity, as well as the SOC and TN contents, which will adversely impact grassland biodiversity conservation and soil C sequestration, and then may intensify the degradation of alpine meadows on the Qinghai–Tibet Plateau. [ABSTRACT FROM AUTHOR]

The carbon balance of the global ecosystems is significantly influenced by the soil organic carbon (SOC) pool in China's terrestrial ecosystems. Nevertheless, the current understanding of the main controlling factors of SOC in different ecosystems and their discrepancies is limited. The goal of this research was to better understand the human and environmental variables affecting SOC in China's terrestrial ecosystems. We designed a conceptual framework using 2674 samples collected from four ecosystems (grasslands, shrublands, wetlands, and croplands) in China during the 2000–2014 period, combining geodetector and multiple regression (MR) approaches to investigate the effects of environmental conditions, human activity, and their interplay on surface SOC (0–20 cm). Results showed that there were large discrepancies in the strength of influencing factors among different ecosystems. Total nitrogen (TN), mean annual temperature (MAT), and bulk density (BD) were the major factors influencing SOC in grasslands. BD, TN, and pH dominated in shrublands. For wetlands, SOC stocks were primarily attributed to maximum temperature (TMMX), MAT, and potential evapotranspiration (PET). Croplands are predominantly controlled by minimum temperature (TMMN), MAT, and TN. These results highlight that natural factors, particularly climatic and soil characteristics, were the dominant factors controlling SOC stocks in China's terrestrial ecosystems. This work also highlights that the interaction of two influencing factors, especially, pairs of soil characteristics factors, pairs of climate and soil characteristics factors, can well explain the drivers of SOC on the surface soil in China. Our study emphasizes the spatial heterogeneity of the factors that influence SOC in terrestrial ecosystems, enhancing knowledge of SOC at the national level, and providing the guideline for devising better policy to improve C sequestration and mitigate climate changes. [ABSTRACT FROM AUTHOR]

Gravel mulch is an agricultural water conservation practice that has been widely used in the semi-arid region of northwest China, but its effectiveness is now lessening due to soil degradation caused by long-term gravel mulching. In this study, we report on a 6-year-long gravel mulch experiment conducted in the northwestern Loess Plateau to evaluate the impact of gravel mulch on soil physicochemical properties and microbial communities, with the objective of clarifying the causes of long-term gravel mulching-induced land degradation. After 6 years mulching, we found that gravel mulched soil contained significantly higher concentrations of total carbon and total organic carbon than non-mulched soil (control). Long-term gravel mulching significantly changed the soil microbial diversity and abundance distribution of bacterial and fungal communities. Notably, the relative abundance of Acidobacteria was significantly higher under gravel mulching than the control (no mulching), being significantly greater in the AG treatment (small-sized gravel, 2-5 mm) than all other treatments. Conversely, the relative abundance of Actinobacteria was significantly lower under gravel mulching than the control, being the lowest in the BG treatment (large-sized gravel, 40-60 mm). At the same time, the relative abundance of Bacteroidetes was significantly lower in AG yet higher in BG vis-à-vis the other treatments. Of the various factors examined, on a 6-year scale, the capture of dust by gravel mulch and altered carbon and nitrogen components in soil play major contributing roles in the compositional change of soil microorganisms. These results suggest that modified soil material input from gravel mulching may be the key factor leading to soil degradation. More long-term experimental studies at different sites are now needed to elucidate the mechanisms responsible for soil degradation under gravel mulching. [ABSTRACT FROM AUTHOR]

Purpose: Temperate herbaceous wetlands have been widely experiencing shrub encroachment due to global climate change and human activities. We attempted to investigate the effect size and pathway of shrub-induced C sequestration in coastal wetlands. Methods: In the shrub-encroached wetlands of the Yellow River Delta, China, two transects were selected randomly, including two landscapes (flat wetland, FW, and tidal ditch wetland, TDW). Based on the distances to shrub Tamarix chinensis, four soil sampling sites (base, mid, edge, and between) for each shrub were determined. We analyzed spatial patterns of soil organic and inorganic carbon (SOC and SIC) and total nitrogen contents (TN) and stable isotope ratios (δ13C and δ15N), evaluated the direct and indirect effects of shrub on SOC and SIC by stepwise regression and structural equation modeling (SEM), and then determined the coupled relationships between soil C and N. Results and discussion: Shrub encroachment increased significantly both SOC (by 67.18%) and SIC (by 9.93%) contents, with higher SOC increase in FW whereas higher SIC increase in TDW. TN had the strongest positive effect on soil carbon (0.797 for SOC and 0.949 for SIC), and that C/N ratio had the second strongest positive influence on SOC (0.716) but negative influence on SIC (−0.567). This suggested a superimposed effect from both TN and C/N ratio on SOC and an offset effect on SIC. Additionally, TN had a greater effect on SOC in FW while clay and silt had a higher effect on SIC in TDW. Both δ13C and δ15N values decreased simultaneously (−0.69‰ and −0.16‰) in TDW while δ13C decreased greatly (−2.36‰) but δ15N increased greatly (0.39‰) in FW. It means that a coupled relationship existed between soil C and N cycling in the former but a decoupled relationship in the latter. Finally, an interaction mechanism was proposed, where the coupled and decoupled relationships between soil C and N was one likely factor which drove higher SIC accumulation in better wetland but higher SOC sequestration in poor one. Conclusions: The presence of shrubs increased SOC and SIC in coastal wetlands with significant landscape effects, resulted in tidal ditch wetland (better wetland) being potential sinks of inorganic carbon, and in flat wetland (nutrient-poor wetland) being significant sinks of organic carbon. The indirect effect of shrub on soil carbon was dominant, which was driven mainly by increasing TN and altering coupled relationships between soil C and N. [ABSTRACT FROM AUTHOR]

Forests worldwide store large quantities of carbon (C), particularly in soils as soil organic C (SOC). In northeastern China, two dominant forest types, secondary mixed forest (MF) and larch plantation forest (LF), cover extensive areas. However, we lack an understanding of the patterns and the mechanisms of SOC storage and stabilization in MF and LF, especially in deep soil layers. This research aims to illustrate the vertical distribution and mineral protection of SOC over soil depth; we also used δ13C values of soil fractions to evaluate SOC stability. Samples from the surface litter (Oi), organic layer (Oa+e), and 0–40 cm mineral soils were collected from both MF and LF plots. We used two different methods to separate bulk soils into distinguished fractions: (1) macro- and micro-aggregates and the non-aggregated fraction, and (2) particulate organic matter (POM) and mineral-associated organic matter (MAOM). The C concentrations, C stocks, and δ13C of all soil fractions were determined. Our findings were as follows: (1) SOC was mainly stored in mineral soils and was 13.6% lower in LF (8609 ± 1180 g C m−2) than MF (9969 ± 2084 g C m−2). (2) In both MF and LF, the SOC stock was mainly stored in aggregates (averaged 92.7%); macroaggregates dominated in the surface layers (Oa+e layer and 0–10 cm) but microaggregates dominated in the deep layers (10–20 cm and 20–40 cm). In mineral soils, MAOM was the dominant fraction of the C stock (averaged 81.6%). (3) The proportion of C distributed in microaggregates and MAOM increased from Oa+e to the 20–40 cm layer. (4) The C/N ratios and δ13C values of MAOM were smaller and heavier compared to those of POM. Our study demonstrated that in both forests, aggregate formation and mineral association predominantly contributed to SOC storage, and large stocks of SOC were distributed in the deep soil. The increasing proportion of SOC in microaggregates and MAOM along the soil depth, most likely derived from microbial turnover and microbial necromass, influenced SOC stability in both forest types. [ABSTRACT FROM AUTHOR]

Little is known about the response of soil respiration components to environmental changes, especially in high-altitude forest ecosystems. To examine the different effects of temperature and moisture on separate soil respiration components, namely autotropic (Ra) and heterotrophic (Rh) respirations, the gap formation method was adopted in a semi-arid highland elm (Ulmus pumila L.) sparse forest, Northwestern China. In 2021, a 9.33 m transect between two elm trees was built, forming a gap of elm sparse forest on the plateau. Soil respiration was measured along the transect between two elm trees. The results showed that the soil respiration under the canopy decreased with increasing distance from the base of the elm, and that the root had no effect on the soil respiration outside the canopy. Here we demonstrated that the mean value of Ra contribution to the total respiration (Rt) is 63%. Results of this study also showed that the temperature sensitivity of Rh (Q10 = 4.29) was much higher than that of Ra (Q10 = 1.40), and that soil moisture (SM) explained the variation of Ra (64.4%) better than that of Rh (49.9%). Our results suggested that the key driver of Rh was soil temperature (ST), and that of Ra was SM in the semi-arid highland elm sparse forest in Northwest China. The gap formation method is helpful to better understand the different responses of Ra and Rh to the variation of ST and SM in elm sparse forest in the semi-arid highland of Northwest China. We highlight that the different responses of Rh and Ra to the same environmental factors should be considered when predicting the future soil carbon cycle. [ABSTRACT FROM AUTHOR]

Grasslands are the main land use types in China, but their reclamation into croplands can influence the terrestrial carbon and, consequently, impact the global carbon balance. The long-term reclamation of alpine-cold grasslands to croplands are expected to decrease the soil organic carbon (SOC) and its fractions. Here, we conducted an in situ systematic study to measure the SOC and its fraction in soils sampled in an alpine-cold grassland with a gradient of cultivation history from 0 to 40 years. The SOC and its fractions significantly decreased after reclamation (P < 0.05), and the changes in the 0-20 cm soil layer were the greatest among the three sampling depths. After 40 years of reclamation, the SOC content and storage at 0-20 cm decreased by 74 and 60%, respectively. The decreases in the soil labile carbon fractions were more rapid and apparent than the SOC, especially the particular organic carbon (POC), which decreased by 82%. The soil humus carbon fractions also decreased, particularly the humic acid carbon (HAC), which decreased by 81%. The reduction rates of SOC and its fractions gradually decreased with an increase in the cultivation history. Besides, the ratios of the optical densities or absorbances of humic acid (HA) and fulvic acid (FA) solutions at 465 and 665 nm (E4/E6 ratios) and the hue coefficient (Δlog K values) which is the logarithm disparity between the 400 and 600 nm absorbance of the HA (FA) substance in the solution gradually decreased, indicating that the quality of the soil humus decreased. The reclamation significantly decreased the SOC and its fractions in the alpine-cold soils, which should not be underestimated in the impact on the terrestrial carbon cycles and balance in the long run. [ABSTRACT FROM AUTHOR]

Organic and inorganic soil fertilizer addition or removal pose significant effects on soil nutrients. As climate change and other anthropogenic factors are causing deprivation in soil nutrient profiles and altering its proper functioning, complete insight into fertilizer modification and its consequences is required for understanding the sustenance of forest ecosystems. In this regard, an experiment was conducted at Liangshui National Nature Reserve, northeast China, in which two forest soil types (i.e., Korean pine plantation and natural Korean pine forest) were evaluated for their response to external fertilizer applications and litter treatments. The litter treatments were litter application as Ck (undisturbed litter), RL (removed litter) and AL (Alter/double litter i.e., litter removed from RL was added in double litter plots), whereas the synthetic fertilizer treatments were Control (No added N and P), Low (5 g N m−2 a−1 + 5 g P m−2 a−1), Medium (15 g N m−2 a−1 + 10 g P m−2 a−1) and High (30 g N m−2 a−1 + 20 g P m−2 a−1). The outcome showed that soil organic carbon (SOC) was directly proportionate to forest litter amounts. Synthetic fertilizers affected soil total nitrogen (STN) and maximum amounts were recorded in plots with H: 30 g N m−2 a−1 + 20 g P m−2 a−1, as 3.03 ± 0.35 g kg−1 in AL. Similarly, altered litter/double was most effective in enhancing the quantity of soil total phosphorus (STP) (0.75 ± 0.04 g kg−1). Soil sampling carried out during the start and end of the experiment showed decreases in the sixth sampling of: SOC (4–23%), STN (7.5-10.8%) and STP (8.51–13.9%). A positive correlation was observed between SOC and total nitrogen; C:N ratio also increased with SOC. Principal component analysis (PCA) on captured a total of 62.1% variability, on the x-axis (35.1%) and on the y-axis (27%). It was concluded that combined application of N and P at the level of 30 g N m−2 a−1 + 20 g P m−2 a−1 under AL (Alter/double litter) treatment level improved soil total N and P content. The results clearly depicted that forest litter is an important source for building up of soil organic matter, however for attaining maximum sustenance capabilities in soil, the continuity of fertilizer application in either form is a prerequisite. [ABSTRACT FROM AUTHOR]

Understanding the influence of microbial taxa and functions on soil carbon (C) and nitrogen (N) cycling, particularly concerning soil aggregate sizes, is crucial for ecosystem management. This study examines the taxonomic and functional dynamics of soil bacterial communities within different aggregate sizes over time. Soil samples from a reclamation forest on the Loess Plateau in North China were collected across reclamation ages of 0, 3, 18, and 28 years. Soil aggregates were categorized into large macro-aggregates (>2000 μm), small macro-aggregates (250-2000 μm), and micro-aggregates (<250 μm) using a modified dry-sieving method. Soil aggregate stability, C and N concentrations, newly derived plant C, enzyme activities, bacterial communities, and functional genes in each aggregate fraction were systematically analyzed. There was a notable increase in soil aggregate stability and a higher proportion of large aggregates was found with increasing forest age. There were significant differences in bacterial community structures, particularly between micro-aggregates and large macro-aggregates and across different forest ages. Reclamation led to an increased abundance of copiotrophic bacterial taxa. Decreases in N-acquiring enzyme activity in micro-aggregates were contrasted by an increase in C, N, and phosphorus (P) acquisition activities in larger aggregates over time. Larger aggregates showed a faster recovery of C and N cycling genes accompanied by a significant enhancement in acetyl-CoA and ammonia oxidation processes, underscoring their importance in soil nutrient cycling. These results highlight the critical role of aggregate size in shaping microbial community structures and functions that influence soil C and N cycling during reclamation and provide new perspectives highlighting the significance of incorporating aggregate size considerations into soil management and reclamation strategies., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Background: Despite the importance of root decomposition in predicting ecosystem responses to future climate change, the effects of branch order on root decomposition and the feedback to soil still remains poorly understood. Here we separated root samples taken from two tree species (Castanopsis fargesii and Schima superba in subtropical forests along the coastal area in eastern China) into four-order classes (1st–2nd order, 3rd order, 4th order, and 5th order) and conducted a 540-day litterbag incubation experiment in laboratory to examine root mass loss, nutrient release, and the influence on soil during decomposition. Results: C. fargesii roots of 1st–2nd and 3rd order decayed more slowly than those of 4th and 5th order, but this pattern was not significant for S. superba. Of all the measured root traits, the decomposition rates correlated best with root C/N ratio, diameter and specific root length (SRL) based on the structural equation modeling. Both tree species and root order exhibited significantly effects on root initial traits. Overall, C. fargesii roots decay faster than S. superba, and this appears to be associated with root initial C quality and N concentration. In addition, root order positively affected root decomposition rates mainly through root diameter and SRL. However, no significant difference was found in C and N content between soils below the litterbag with different-order roots. Conclusions: Our findings suggest the effects of branch order on root decomposition are dependent on tree species. Moreover, root morphological properties might also be the controlling factor in root decay besides root chemistry fractions. Overall, the integrative effects should be considered to improve our understanding of the fate of fine-root litter and their contribution to soil C and N pool. [ABSTRACT FROM AUTHOR]

Theory and experiments support that plant invasions largely impact aboveground biodiversity and function. Yet, much less is known on the influence of plant invasions on the structure and function of the soil microbiome of coastal wetlands, one of the largest major reservoirs of biodiversity and carbon on Earth. We studied the continental-scale invasion of Spartina alterniflora across 2451 km of Chinese coastlines as our model-system and found that S. alterniflora invasion can largely influence the soil microbiome (across six depths from 0 to 100 cm), compared with the most common microhabitat found before invasion (mudflats, Mud). In detail, S. alterniflora invasion was not only positively associated with bacterial richness but also resulted in important biotic homogenization of bacterial communities, suggesting that plant invasion can lead to important continental scale trade-offs in the soil microbiome. We found that plant invasion changed the community composition of soil bacterial communities across the soil profile. Moreover, the bacterial communities associated with S. alterniflora invasions where less responsive to climatic changes than those in native Mud microhabitats, suggesting that these new microbial communities might become more dominant under climate change. Plant invasion also resulted in important reductions in the complexity and stability of microbial networks, decoupling the associations between microbes and carbon pools. Taken together, our results indicated that plant invasions can largely influence the microbiome of coastal wetlands at the scale of China, representing the first continental-scale example on how plant invasions can reshuffle the soil microbiome, with consequences for the myriad of functions that they support. [ABSTRACT FROM AUTHOR]

Large quantities of semiconductor minerals on soil surfaces have a sensitive photoelectric response. These semiconductor minerals generate photo-electrons and photo-hole pairs that can stimulate soil oxidation–reduction reactions when exposed to sunlight. We speculated that the photocatalysis of semiconductor minerals would affect soil carbon cycles. As the main component of the carbon cycle, soil respiration from paddy soil is often ignored. Five rice cropping areas in China were chosen for soil sampling. Semiconductor minerals were measured, and three main semiconductor minerals including hematile, rutile, and manganosite were identified in the paddy soils. The identified semiconductor minerals consisted of iron, manganese, and titanium oxides. Content of Fe2O3, TiO2, and MnO in the sampled soil was between 4.21–14%, 0.91–2.72%, and 0.02–0.22%, respectively. Most abundant semiconductor mineral was found in the DBDJ rice cropping area in Jilin province, with the highest content of Fe2O3 of 14%. Soils from the five main rice cropping areas were also identified as having strong photoelectric response characteristics. The highest photoelectric response was found in the DBDJ rice cropping area in Jilin province with a maximum photocurrent density of 0.48 μA/cm2. Soil respiration was monitored under both dark and light (3,000 lux light density) conditions. Soil respiration rates in the five regions were (from highest to lowest): DBDJ > XNDJ > XBDJ > HZSJ > HNSJ. Soil respiration was positively correlated with semiconductor mineral content, and soil respiration was higher under the light treatment than the dark treatment in every rice cropping area. This result suggested that soil respiration was stimulated by semiconductor mineral photocatalysis. This analysis provided indirect evidence of the effect semiconductor mineral photocatalysis has on the carbon cycle within paddy soils, while exploring carbon conversion mechanisms that could provide a new perspective on the soil carbon cycle. [ABSTRACT FROM AUTHOR]

Backgrounds: A large-scale ecological restoration project was initiated in the 1990s in southwest China, which is one of the largest areas of rocky desertification globally. However, the influence and potential mechanisms of vegetation restoration on soil carbon(C) sequestration in karst and non-karst regions remains unclear. Methods: Based on field investigation and multi-source data synthesis, the mechanisms of soil C sequestration were investigated to determine the most important variables affecting the rate of soil C change (Rs) in southwest China. Results: Our results show significant differences in soil C sequestration between karst and non-karst regions with faster and longer C sequestration occurring in karst regions. In these areas, Rs was approximately 31% higher than in non-karst soils. The Rs of shrubland, grassland and cropland sites in karst areas was significantly higher than that observed in non-karst areas. We found that temperatures were the primary factor inhibiting soil C sequestration instead of precipitation. The total effect of nitrogen (N) on Rs was positive in both karst and non-karst regions. Conclusions: Phosphorus was the dominant factor limiting the use of N by vegetation in karst regions and then resulting in limitation of C sequestration. The results indicated that soil C storage may increase intermittently due to combination of karst environment and climate change in southwest China in future. [ABSTRACT FROM AUTHOR]

Char materials (e.g., hydrochar) can enhance carbon sequestration, improve soil quality and modulate soil microbial communities to recuperate soil health. However, little is known about the soil organic carbon (SOC) content, as well as the microbial communities and co-occurrence networks in response to hydrochar amendment in an inshore saline soil. Here, the effect of Sesbania cannabina (a halophyte) straw derived hydrochar (SHC) amendment on SOC and labile organic carbon (LOC) fractions and the potential associations among SOC content change, soil C-cycling enzyme activities and microbial communities were illustrated using a pot experiment. SHC effectively improved the contents of SOC and LOC, particularly particulate organic carbon (POC), and stimulated the activities of C-cycling enzymes. Furthermore, SHC induced shift in microbial community compositions and co-occurrence networks, result in decrease in relative abundance of Actinobacteriota and its corresponding ecological cluster, which may favor SOC accumulation. Functional annotation of prokaryotic taxa (FAPROTAX) analysis also revealed a decrease in microbial ecological function related to carbon degradation. These findings provided a deeper insight about the hydrochar-induced SOC enhancement and suggested an efficient approach to improve C sequestration and improve soil health in the coastal salt-affected soil., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier Inc.)

Irrigation has become one of the main approaches to improve agricultural production in an arid area. The variation of soil moisture after irrigation has the potential to affect soil microbial community composition and soil organic carbon (SOC) storage, and thus, the imbalances in the terrestrial ecosystem carbon cycle. However, the impact of long‐term irrigation on the relationships between soil microbial community and SOC sequestration in semiarid agroecosystems is still poorly understood. We took advantage of a 7‐year irrigation experiment in a winter wheat‐maize rotation system in northern China, whereby the non‐irrigation was subject to rain‐fed conditions. We aimed to investigate the effects of long‐term irrigation on soil microbial communities and their linkages with soil carbon sequestration. Seven years of irrigation significantly increased soil moisture content by 39% but decreased SOC concentration of topsoil (0–20 cm) by 4.2% on average across all sampling times. The responses of soil microbial communities to irrigation were highly taxa dependent. Irrigation significantly decreased fungal biomass, fungal‐to‐bacterial ratio and Gram‐positive‐to‐Gram‐negative bacterial ratio, and did not affect the bacterial community biomass. The decreased SOC concentration under the long‐term irrigation was mainly caused by the changes in the ratio of fungi‐to‐bacteria. Our findings highlight the important role of soil fungal‐to‐bacterial ratio in mediating the response of SOC dynamics to a future drier climate in semiarid agricultural ecosystems. Highlights: Irrigation influences the soil microbial community and carbon stock in semiarid agroecosystems. Highlights the role of fungi:bacteria ratio in mediating the response of SOC dynamics to irrigation Long‐term irrigation decreased soil carbon content by changing the microbial community. Reduced SOC storage after irrigation was due to the decreased ratio between fungi and bacteria. [ABSTRACT FROM AUTHOR]

Afforestation is recommended as an effective approach for carbon sequestration and environmental benefits. However, it remains less clear, and sometimes controversial, regarding how afforestation may impact soil inorganic carbon (SIC), a crucial component of the ecosystem carbon pool. Using field data from 619 afforested plots and 163 control plots across northern China, we here investigated the relative and absolute differences in SIC between afforested and corresponding control plots. Our results suggested that afforestation increased SIC in acidic soils, while decreased SIC in alkaline soils. Fitting a linear mixed model and further a structure equation model, we found that afforestation‐induced soil pH change was the most significant factor regulating SIC responses. In particular, SIC was more sensitive to pH change in more arid areas, where both soil pH and SIC stocks were high. Other factors could indirectly affect SIC responses to afforestation through modulating soil pH and soil organic carbon (SOC) dynamics. Moreover, afforestation‐induced SIC changes also varied considerably among different species of tree plantations and across different soil depths. Importantly, in plantations of Pinus sylvestris var. mongholica, Pinus tabuliformis, and Populus spp., changes in SIC caused by afforestation were even comparable to that in SOC. Overall, our findings provide a data‐based understanding on the comprehensive soil carbon dynamics following afforestation and its underlying mechanisms. With the increased use of afforestation and reforestation as nature‐based solutions to climate change, their associated impacts on SIC need to be taken into account, especially in SIC‐rich areas. Key Points: We conducted an extensive field survey investigating the impact of afforestation on soil inorganic carbon (SIC)Soil pH was a key variable mediating SIC responses to afforestation, which enhanced SIC in acidic soils but decreased SIC in alkaline soilsSIC responses to afforestation also showed high variabilities among different species of tree plantations and across soil depths [ABSTRACT FROM AUTHOR]

The carbon pool is changing in afforestation ecosystems, which vary in their duration since establishment, in many semiarid sand regions. Understanding this is important for the management of the planted forest. The present study explored the dynamics of afforested forest carbon pool in a semiarid sandy ecosystem, northwest China. We studied afforested forests of pine (Pinus sylvestris) of five afforestation ages (20, 30, 40, 50, and 60 years since planting, and bare sand as control), the carbon storage and carbon sequestration rate of the forest aboveground biomass layer, surface litter layer, and soil layer (0–50 cm) were calculated, and the soil water content and soil organic carbon of 0–400 cm soil depth were measured. The results showed that the carbon sequestration rate was highest after 20–30 years, with 0.58 Mg C ha−1 yr−1 in the soil layer (0–50 cm). We found a rate of 0.13 Mg C ha−1 yr−1 in the surface litter layer, and a rate of 20.79 Mg C ha−1 yr−1 in the forest aboveground biomass layer. The carbon storage of the forest aboveground biomass layer was highest after 30–40 years, and the carbon storage of the surface litter increased with time. In the soil layer, the carbon storage at 0–10 cm depth was highest after 60 years, the carbon storage at 20–50 cm depth increased soon after afforestation and then decreased afterward with increasing afforestation ages with the maximum for 20‐50 cm occurring after 30–40 years. The total carbon storage [the forest aboveground biomass layer, surface litter layer and soil layer (0‐50 cm)] was higher when afforestation ages reached around 30 years, after that it decreased with increasing afforestation age. Our research improves the understanding of the P. sylvestris forest ecosystem carbon sequestration in a semiarid sandy area. [ABSTRACT FROM AUTHOR]

Hydrological connectivity has significant effects on the functions of estuarine wetland ecosystem. This study aimed to examine the dynamics of hydrological connectivity and its impact on soil carbon pool in the Yellow River Delta, China. We calculated the hydrological connectivity based on the hydraulic resistance and graph theory, and measured soil total carbon and organic carbon under four different hydrological connectivity gradients (I 0–0.03, II 0.03–0.06, III 0.06–0.12, IV 0.12–0.39). The results showed that hydrological connectivity increased in the north shore of the Yellow River and the south tidal flat from 2007 to 2018, which concentrated in the mainstream of the Yellow River and the tidal creek. High hydrological connectivity was maintained in the wetland restoration area. The soil total carbon storage and organic carbon storage significantly increased with increasing hydrological connectivity from I to I gradient and decreased in IV gradient. The highest soil total carbon storage of 0–30 cm depth was 5172.34 g/m2, and organic carbon storage 2764.31 g/m2 in III gradient. The hydrological connectivity changed with temporal and spatial change during 2007–2018 and had a noticeable impact on soil carbon storage in the Yellow River Delta. The results indicated that appropriate hydrological connectivity, i.e. 0.08, could effectively promote soil carbon storage. [ABSTRACT FROM AUTHOR]

The relationship between plant diversity and the ecosystem carbon pool is important for understanding the role of biodiversity in regulating ecosystem functions. However, it is not clear how the relationship between plant diversity and soil carbon content changes under different grassland use patterns. In a 3-year study from 2013 to 2015, we investigated plant diversity and soil total carbon (TC) content of grasslands in northern China under different grassland utilization methods (grazing, mowing, and enclosure) and climatic conditions. Shannon-Wiener and Species richness index of grassland were significantly decreased by grazing and mowing. Plant diversity was positively correlated with annual precipitation (AP) and negatively correlated with annual mean temperature (AMT). AP was the primary regulator of plant diversity. Grazing and mowing decreased TC levels in grasslands compared with enclosures, especially in topsoil (0-20 cm). The average TC content was decreased by 58 % and 36 % in the 0-10 cm soil layer, while it was decreased by 68 % and 39 % in 10-20 cm soil layer. TC was positively correlated with AP and negatively correlated with AMT. Principal component analysis (PCA) showed that plant diversity was positively correlated with soil TC, and the correlation decreased with an increase in the soil depth. Overall, this study provides a theoretical basis for predicting soil carbon storage in grasslands under human disturbances and climate change impacts., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024. Published by Elsevier B.V.)

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Intensive coastal wetland reclamation in China followed by agricultural use had significant impacts on soil carbon (C) dynamics due to the alterations in soil hydrology and physicochemical properties. The changes in C and its driving factors in reclaimed soils generally concentrated on soil organic C (SOC) and soil inorganic C (SIC) as major subpools of soil C, but this topic has received little attention. In this study, we have assessed the changes in SOC and SIC concentrations (0–20 cm) with reclamation duration and land use change based on 746 surface soil samples collected from three typical reclamation areas (with differences in sediment sources) in eastern China. Key factors driving SOC and SIC dynamics were identified using a random forest model (RF). The results revealed similar SOC concentration (7.24–7.69 g kg−1) and different SIC concentration (7.25–10.9 g kg−1) for the three study areas. Overall, SOC increased with reclamation duration, suggesting a positive impact of tidal flat reclamation on SOC accumulation. For SIC, slight increases in the younger land and dramatic decreases in the older land were observed, indicating a fast IC turnover time. The land impacted strongly by human activities had higher SOC than natural tidal flats. Compared with upland soil, paddy soil resulted in greater OC (except for 10 years reclaimed land in Cixi) and comparable levels of IC. Soil nutrient levels (the concentrations of nitrogen and phosphorus) were determined to be important factors for SOC in reclaimed lands. Soil CaO was determined to be the factor with the highest importance in controlling SIC dynamics in reclaimed lands. More attention should be given to the quality of the OC sequestrated by reclaimed soils. • Organic and inorganic carbon (OC and IC) dynamics of reclaimed soils were studied. • Key factors driving for soil OC and soil IC were measured using random forest method. • Paddy soil management was practical for carbon sequestration on reclaimed lands. • More attention should be given to the quality of the OC sequestered by reclaimed soil. [ABSTRACT FROM AUTHOR]

Ecological restoration increases biodiversity and carbon and nitrogen accumulation. Although soil enzyme activities are critical to element cycling and plant diversity and productivity in natural habitats, little is known regarding the effects of ecological restoration on the activities of soil resident enzymes. We investigated the influence of ecosystem restoration on microbial carbon and nitrogen dynamics in soil, as well as the functionality of five enzymes (catalase, dehydrogenase, polyphenol oxidase, urease, and invertase) via the extraction of samples from stands that were subjected to continuous anthropogenic disturbances (i.e., recurring fuelwood collection and domestic animal grazing) in contrast to samples obtained from stands which were left undisturbed for 6, 11, 21, and 31 years in the subtropical forests of China. We found that soil microbial biomass carbon and nitrogen increased with time since restoration, and the activities of catalase, dehydrogenase, invertase, urease, and polyphenol oxidase were amplified in the undisturbed stands following 11 years of restoration, which continued at high levels or decreased thereafter. Redundancy analysis revealed that enzyme activities were augmented in response to biomass inputs from aboveground litterfall and fine root mortality and were positively related to soil carbon and available nitrogen, phosphorus, and potassium contents. Our results highlight the multiple links between increased aboveground and belowground inputs, the abundance of soil-dwelling microorganisms and their enzyme activities, and their contributions to soil carbon and nutrient cycling following the ecological restoration of degraded subtropical forests. • Soil microbial carbon and nitrogen increase following ecological restoration. • Soil enzyme activities increase following ecological restoration. • Litterfall production and fine root mortality contribute to soil enzyme activities. • Soil carbon and available nutrients are positively associated with enzyme activities. [ABSTRACT FROM AUTHOR]

Abstract Grassland recovery from degradation is increasingly occurring worldwide. Diverse managements have been considered as effective ways to restore degraded grassland, but it remains unclear how semi-arid grasslands respond to long-term grazing exclusion and fenced mowing. Here, a study was conducted under open grazing, grazing exclusion and fenced mowing in a semi-arid grassland on the Loess Plateau. We measured plant species composition and diversity, plant production, surface litter and soil water and carbon content. Shifts in grassland management led to significant divergence in plant community composition. Long-term grazing exclusion (35 years) significantly increased plant biomass, surface litter, soil water and carbon storage, but suppressed plant diversity compared to open grazing. Conversely, fenced mowing significantly increased plant diversity accompanying with a weak effect on soil carbon. Moreover, mowing significantly reduced surface litter and soil moisture, which have strong implications for nutrient depletion and soil drying. Our results suggest that introducing disturbances are necessary to safeguard biodiversity, and continuous mowing (5 years) belongs to over exploitation of the long-term protected grassland. Therefore, it is essential to optimize management with dual objectives of biodiversity and soil carbon sequestration in the future. Highlights • Three representative management-related steppe conditions were evaluated. • Long-term grazing exclusion replenished SOC but decreased plant diversity. • Fenced mowing safeguarded plant diversity but induced soil drying. [ABSTRACT FROM AUTHOR]

• n -Alkyl lipids were investigated in cultivated Sphagnum and the underlying soil, together with natural Sphagnum. • Distributions of n -alkyl lipids are similar in cultivated and natural Sphagnum growing in the same region. • δ13C values of mid-chain n -alkanes are significantly negative in the cultivated Sphagnum. • Lipids have the potential to trace the environmental influences of Sphagnum cultivation in mineral soil. Sphagnum , a crucial peat-forming plant, is essential for sustaining the ecosystem and counteracting climate change. In recent years, attempts have been made to cultivate Sphagnum commercially to reduce the environmental impacts of harvesting the natural Sphagnum. However, research on the distribution of lipids in cultivated Sphagnum and their potential for preservation potential in the underlying soil is still limited. This study examined the distribution of n -alkyl lipids and the carbon isotope composition of n -alkanes in both natural and cultivated Sphagnum , as well as the underlying topsoil in southwestern China. Results show that the distributions of n -alkyl lipids in the cultivated Sphagnum are similar to those of the natural Sphagnum in the same region. Additionally, the δ13C values of mid-chain n -alkanes (C 23 and C 25) in the cultivated Sphagnum are significantly negative compared to those of long-chain homologs (C 29 and C 31 ; one-way ANOVA, p < 0.05), indicating that symbiotic methanotrophs are relatively active in the cultivated Sphagnum. Furthermore, the n -fatty acids and n -alkan-2-ones in the topsoil are mainly imported from Sphagnum , while the n -alkanes in the topsoil may originate from both Sphagnum and vascular plants. These findings contribute to a better understanding of the ecological benefits of Sphagnum cultivation and the contribution and fate of Sphagnum -derived carbon in soil profiles. [ABSTRACT FROM AUTHOR]

• R SOC and R N in both top- and sub-soil following GE were studied in the Loess Plateau of China. • GE increased SOC and N stocks at soil layer of 0–60 cm. • MAT rather than MAP is the main factor in driving R SOC and R N. • R SOC in each soil layer is also correlated with altitude. • The strong coupling between R SOC and R N induced no change in C/N with duration of GE. Enhancement of soil organic carbon (SOC) and nitrogen (N) storage in degraded ecosystems is of great significance for improving soil quality and mitigating climate change. Grazing exclusion is an effective management practice to restore degraded ecosystems in drylands. However, the spatio-temporal dynamics and regulating factors of SOC and N sequestration in degraded ecosystems following grazing exclusion has not been clearly explored. Using synthesized data from 38 peer-reviewed publications, we investigated the rates of SOC (R SOC) and soil total N (R N) stock changes and their controlling factors following grazing exclusion in the Loess Plateau of China. Grazing exclusion significantly increased SOC and total N stock in most sites. The average R SOC was 0.57, 0.64 and 0.7 Mg ha–1yr−1 and the average R N was 0.033, 0.031 and 0.036 Mg ha–1yr−1 at 0–20, 20–40 and 40–60 cm soil depths, respectively. R SOC showed a Poisson function relation with the duration of grazing exclusion. R SOC and R N did not significantly change with mean annual precipitation, but they were negatively correlated with mean annual temperature at 0–20 cm. R SOC at each soil depth was positively correlated with altitude. The strong coupling relationship between R SOC and R N resulted in no significant change in the ratio of SOC to total N between grazing exclusion and grazing sites over time. The results show that altitude, age of GE and initial SOC and N contents rather than precipitation controls these processes in the Loess Plateau. Grazing exclusion promotes SOC and N sequestrations more than 30 years in the degraded lands of the Loess Plateau. The inherent increase of soil N would be beneficial to soil carbon sequestration during the recovery process. [ABSTRACT FROM AUTHOR]

To evaluate the influence of wetland reclamation on vertical distribution of carbon and nitrogen in coastal wetland soils, we measured the soil organic carbon (SOC), soil total nitrogen (STN) and selected soil properties at five sampling plots (reed marsh, paddy field, corn field, forest land and oil-polluted wetland) in the Liaohe River estuary in September 2013. The results showed that reclamation significantly changed the contents of SOC and STN in the Liaohe River estuary (P < 0.001). The SOC concentrations were in the order: oil-polluted wetland > corn field > paddy field > forest land > reed marsh, with mean values of 52.17, 13.14, 11.46, 6.44 and 6.16 g/kg, respectively. STN followed a similar order as SOC, with mean values of 1351.14, 741.04, 632.32, 496.17 and 390.90 mg/kg, respectively. Interaction of reclamation types and soil depth had significant effects on SOC and STN, while soil depth had significant effects on SOC, but not on STN. The contents of SOC and STN were negatively correlated with pH and redox potential (Eh) in reed marsh and corn field, while the SOC and STN in paddy field had positive correlations with electrical conductivity (EC). Dissolved organic carbon (DOC), ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3--N) were also significantly changed by human activities. NH4+-N and NO3--N increased to different degrees, and forest land had the highest NO3--N concentration and lowest DOC concentration, which could have been caused by differences in soil aeration and fertilization. Overall, the results indicate that reed harvest increased soil carbon and nitrogen release in the Liaohe River Estuary, while oil pollution significantly increased the SOC and STN; however, these cannot be used as indicators of soil fertility and quality because of the serious oil pollution. [ABSTRACT FROM AUTHOR]

Unraveling the distributions and controls of soil carbon (C) and nitrogen (N) accumulation is conducive to providing guidance for sustainable ecosystem management. Although the factors that affect soil C and N accumulation have been widely investigated, the relative importance of these factors and whether they confer direct or indirect effects remain unclear. Herein, we examined the distributions of soil organic carbon (SOC), soil inorganic carbon (SIC), and total nitrogen (TN) stocks across the 0–200 cm soil profiles in grasslands, forestlands, and shrublands on the Loess Plateau. Moreover, we determined the relative contributions of land use, topography, and soil properties (texture, water, phosphorus, and available nitrogen) to their variations. The results showed that with increasing soil depth, SOC and TN stocks decreased, while SIC stocks fluctuated. However, large amounts of SOC, SIC, and TN were stored in the deep soil layers (100–200 cm), with values of 3.06, 26.63, and 0.50 kg/m2, respectively. In the 0–200 cm soil layers, the total SIC stock was 53.40 kg/m2 and was 6.8 times higher than the total SOC stock. Among different plant communities, grasslands had the highest SIC stock (54.83 kg/m2), while Armeniaca sibirica and Robinia pseudoacacia had the highest SOC stock (10.06 kg/m2) and TN stock (1.49 kg/m2), respectively. Furthermore, approximately 85% of the variations in SOC, SIC, and TN stocks were jointly affected by land use, topography, and soil properties, in which soil properties acted as the most important driving factors, followed by topography and land use. In particular, topography affected SOC, SIC, and TN stocks mainly through its effects on soil texture and water. Overall, vegetation restoration scenarios incorporating grasslands and Robinia pseudoacacia are highly recommended and should be tailored according to specific topographic features. • SIC stock was 6.8 times higher than SOC stock in the 0–200 cm soil layers. • Grasslands performed better in soil C accumulation than forests and shrubs. • Land use, soil property, and topography explained 80% of the changes in C and N. • Land use played a less important role in affecting C and N than topography. • Topography affected soil C and N accumulation by influencing soil clay and water. [ABSTRACT FROM AUTHOR]

The effect of livestock grazing on grassland degradation and the resulting impact on soil carbon concentration is an important factor in carbon estimation. We addressed this issue using field observations and laboratory analysis of samples from Tibetan grassland. Based on the field measurements, we investigated the soil organic carbon (SOC) and soil inorganic carbon (SIC) under two contrasting degradation states: lightly or non-degraded grasslands (LDG) and heavily degraded grasslands (HDG). We assessed their relationships with environmental factors using data collected from 99 sites across Northern Tibet during 2011-2012. Data were analyzed using a linear mixed-effects model and one-way ANOVA. The results showed that: (1) SOC concentration decreased and SIC concentration increased following grassland degradation, especially at soil depths in the range of 0-10 cm ( P < 0.05); (2) the major environmental factors affecting SOC and SIC were soil pH and plant biomass; (3) spatially, the SOC density increased with the mean annual temperature and mean annual precipitation, whereas SIC exhibited the opposite trend; (4) the SOC density increased at first and then decreased with increasing grazing intensity, with an opposite trend in SIC; and (5) soil carbon storage in this region was 0.14 Pg smaller in the HDG than in the LDG. This study suggests that grassland degradation can significantly affect the vertical distribution and storage of SOC and SIC. The carbon sequestration capacity of the top 100 cm of soil in Northern Tibet was estimated as 0.14 Pg. [ABSTRACT FROM AUTHOR]

The impact of land-use and land-cover change (LULCC) on ecosystem carbon (C) dynamics has been previously documented at local and global scales, but uncertainty persists for coastal wetlands due to geographical variability and field data limitations. Field-based assessments of plant and soil C contents and stocks of various LULCC types were conducted in nine regions along the coastline of China (21°-40°N). These regions cover natural coastal wetlands (NWs, including salt marshes and mangroves) and former wetlands converted to different LULCC types, including reclaimed wetlands (RWs), dry farmlands (DFs), paddy fields (PFs) and aquaculture ponds (APs). The results showed that LULCC generally decreased the C contents and stocks of the plant-soil system by 29.6 % ± 2.5 % and 40.4 % ± 9.2 %, respectively, while it slightly increased the soil inorganic C contents and stocks. Wetlands converted to APs and RWs lost greater ecosystem organic C stocks (EOC, sum of plants and top 30 cm of soil organic C stocks) than other LULCC types. The annual potential CO 2 emissions estimated from EOC loss depended on the LULCC type, with an average emission of 7.92 ± 2.94 Mg CO 2 -eq ha -1  yr -1 . The change rate of EOC in all LULCC types showed a significantly deceasing trend with increasing latitude (p < 0.05). The loss of EOC due to LULCC was larger in mangroves than in salt marshes. The results showed that the response of plant and soil C variables to LULCC was mainly related to differences in plant biomass, median grain size, soil water content and soil NH 4 + -N content. This study emphasized the importance of LULCC in triggering C loss in natural coastal wetlands, which strengthens the greenhouse effect. We suggest that the current land-based climate models and climate mitigation policies must account for specific land-use types and their associated land management practices to achieve more effective emission reduction., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

The temporal pattern of carbon stock changes in response to grazing exclusion (GE) is important for grassland ecosystem restoration policy. The carbon stock change rate is the quotient computed by dividing the change in carbon stock after GE by GE duration. We modeled varying carbon stock change rates with GE durations based on data from a meta-analysis by Deng et al. (2017). We found that the close relationship between the carbon stock change rate and GE duration was mostly driven by GE duration in the denominator, rather than by carbon stock changes in the numerator. We argue that Deng et al.'s conclusion that the exponential decay trend varies with GE duration was inaccurate and that it was misleading to suggest there is a temporal pattern to carbon stock changes that is associated with GE duration. Their model may further encourage GE-based policy that includes fencing as a major practice of grassland restoration. However, this practice yields clearly negative impacts on herders' livelihoods, animal husbandry, pastoral social development and wildlife protection. [ABSTRACT FROM AUTHOR]

The mid-Paleozoic colonization of land by plants induced profound changes in the Earth's surface environments. However, it remains poorly understood how the earliest vascular plants, arising during the Silurian and Devonian periods, adapted to and functioned in ancient drylands. Today, drylands occupy ~45% of the Earth's land surface and support diverse ecosystems forming the Earth's most extensive biome. By contrast, only sparse records of dryland systems have been documented from Silurian- and Devonian-aged deposits, and furthermore, in most cases, the evidence for recognizing major plant types is compromised by poor preservation potential of organic matter in such dry environments. Here, we recognize an Early Devonian dryland river system represented by the Guijiatun Formation, Qujing, Yunnan, South China, based on an integrative study combining paleopedology, geochemistry, and paleobotany. This formation contains diverse and abundant redbed calcareous paleosols, most being classified as Calcisols. Such paleosols are interpreted as developing within well-drained landscapes that experienced a semiarid climate with seasonal wet-dry cycles, and are geochemically characterized by the subsurface accumulation and reorganization of pedogenic carbonates. Extensive plant traces are preserved in most of the paleosols observed in the Guijiatun Formation and show K- or H-shaped branching structures that are morphometrically comparable to the belowground rhizomes of zosterophyllopsids and early lycopsids. These plant-bearing paleosols provide direct evidence for the development of primitive vegetation on drylands. The soil inorganic carbon (SIC) contents stored as Ca-Mg carbonates in the Guijiatun paleosols are estimated at 38 ± 8 g C kg−1, comparable to the highest levels of present-day dryland ecosystems. We argue that dryland floras could have been a significant component of the Early Devonian landscapes, controlling the retention of both mobile elements (Ca and Mg) and fine-grained sediment on land, and mantling and protecting buried soil carbon against erosion. [ABSTRACT FROM AUTHOR]

• We produced yearly maps of SOC to 1 m depth in China for 1982–2019 at a 1 km resolution. • The estimated SOC storage ranged from 89.03 to 97.41 Pg C and showed a slight increase over time. • Seventeen percent of all areas exhibited a substantial decrease in SOC since 1982. • We mapped the spatial distribution of the effects of environmental factors on SOC change. • Different factors drive SOC changes in different spatial domains. The evaluation of soil organic carbon (SOC) dynamics and its driving factors is important for developing sustainable soil C sequestration practices. A key challenge is the lack of a time series of spatially explicit SOC estimates; most previous SOC estimates are static. In this study, we applied a digital soil mapping framework to model the relationship between SOC and environmental factors based on a combined dataset of 4695 soil samples collected in China from the early 1980 s and during the 2000–2014 period. We predicted the annual SOC distribution at a depth of 0–100 cm at a 1 km resolution for China between 1982 and 2019. We mapped trends of SOC change and identified change hotspots. To obtain the pixel-level association between SOC change and environmental factors, we used a linear function to quantify the contribution of individual predictors to SOC change. The results show that the accuracy of SOC prediction is acceptable, with a mean R2 value of 0.58 for validation. SOC storage in China was estimated to range from 89.03 to 97.41 Pg C and showed a slight increase (slope = 0.024 Pg C/yr) from 1982 to 2019. Specifically, two distinct phases of SOC were identified as follows: (1) from 1982 to 2004, a considerable decline occurred, which was mainly driven by increased temperature; (2) from 2004 to 2019, SOC increased slowly, resulting from the contribution of greening to sustaining C sequestration in soils under warming conditions. Approximately 17 % of all areas have been characterized by a significant decrease in SOC since 1982, predominantly in central and western China. Environmental controls exhibited large spatial variation, where approximately 69 % of all areas were predominantly controlled by climate factors. For grasslands, the SOC losses in northern China were largely driven by temperature and precipitation, while the SOC losses were primarily attributed to decreased organic inputs driven by grassland degradation on the Tibetan Plateau. Policy-driven land use change has led to an increase in SOC in some cropland areas (e.g., northeast and east China). The implementation of ecological restoration has shown a positive influence on SOC sequestration. This study highlights the diverse spatial patterns and heterogeneity of SOC changes and their controls. Given this spatial differentiation, spatially explicit assessments of soil C dynamics are important for the formulation of regional soil-based mitigation strategies and guidance for effective restoration interventions based on geographic location. [ABSTRACT FROM AUTHOR]

Based on the Terrestrial Ecosystem Model (TEM 5.0), together with the data of climate (temperature, precipitation and solar radiation) and environment (grassland vegetation types, soil texture, altitude, longitude and latitude, and atmospheric CO2 concentration data), the spatiotemporal variations of carbon storage and density, and their controlling factors were discussed in this paper. The results indicated that: (1) the total carbon storage of China's grasslands with a total area of 394.93×10 km was 59.47 Pg C. Among them, there were 3.15 Pg C in vegetation and 56.32 Pg C in soil carbon. China's grasslands covering 7.0-11.3% of the total world's grassland area had 1.3-11.3% of the vegetation carbon and 9.7-22.5% of the soil carbon in the world grasslands. The total carbon storage increased from 59.13 to 60.16 Pg C during 1961-2013 with an increasing rate of 19.4 Tg C yr. (2) The grasslands in the Qinghai-Tibetan Plateau contributed most to the total carbon storage during 1961-2013, accounting for 63.2% of the total grassland carbon storage, followed by Xinjiang grasslands (15.8%) and Inner Mongolia grasslands (11.1%). (3) The vegetation carbon storage showed an increasing trend, with the average annual growth rate of 9.62 Tg C yr during 1961-2013, and temperature was the main determinant factor, explaining approximately 85% of its variation. The vegetation carbon storage showed an increasing trend in most grassland regions, however, a decreasing trend in the central grassland in the southern China, the western and central parts of the Inner Mongolian grasslands as well as some parts on the Qinghai-Tibetan Plateau. The soil carbon storage showed a significantly increasing trend with a rate of 7.96 Tg C yr, which resulted from the interaction of more precipitation and low temperature in the 1980s and 1990s. Among them, precipitation was the main determinant factor of increasing soil carbon increases of China's grasslands. [ABSTRACT FROM AUTHOR]

Converting secondary natural forests (SFs) to Chinese fir plantations (CFPs) represents one of the most important (8.9 million ha) land use changes in subtropical China. This study estimated both biomass and soil C stocks in a SF and a CFP that was converted from a SF, to quantify the effects of land use change on ecosystem C stock. After the forest conversion, biomass C in the CFP (73 Mg·ha−1) was significantly lower than that of the SF (114 Mg·ha−1). Soil organic C content and stock decreased with increasing soil depth, and the soil C stock in the 0–10 cm layer accounted for more than one third of the total soil C stock over 0–50 cm, emphasizing the importance of management of the top soil to reduce the soil C loss. Total ecosystem C stock of the SF and the CFP was 318 and 200 Mg·ha−1, respectively, 64% of which was soil C for both stands (205 Mg·ha−1 for the SF and 127 Mg·ha−1 for the CFP). This indicates that land use change from the SF to the CFP significantly decreased ecosystem C stock and highlights the importance of managing soil C. [ABSTRACT FROM AUTHOR]

Although fencing is an effective restoration strategy used to achieve the global sustainability of grassland ecosystem, it is unclear from the literature whether fencing results in positive effects on soil physicochemical properties, plant diversity and the relationship between soil particle and soil chemical properties in a desert steppe on the Loess Plateau. Therefore, we selected fenced communities and grazed communities to study the effects of grazing exclusion on desert grassland on the Loess Plateau in China. Our results indicate that plant coverage, plant height, richness index, above- and below-ground biomass, root/shoot ratio, the number of grasses and the number of perennials increased significantly, whereas litter biomass, the number of forbs and annuals significantly decreased after approximately 12 years of fencing. Fencing also resulted in marked increases in ammonium nitrogen (AN) in the 0–10 cm soil depth, soil organic carbon (SOC), total nitrogen (TN), nitrate nitrogen (NN), clay and silt in the 0–30 cm soil depth and soil total phosphorus (TP) in 0–100 cm soil depth. Our results also indicated that SOC, TN, NN, clay, silt, sand and belowground biomass were significantly affected by land use type, soil layer and their interaction between land use type and soil layer. However, AN was affected by only land use type, and TP was affected by land use type and soil layer but not their interaction. In addition, there was s significant correlation between soil chemical properties (SOC, TN, TP, NN, AN) and soil particles (silt, clay and sand) in the 0–5 cm soil depth. As part of our ongoing research, this paper can produce substantial ecological benefits by contributing to the development of a more scientific strategy for grassland management on the Loess Plateau. [ABSTRACT FROM AUTHOR]

Grazing exclusion ( GE) is considered to be an effective approach to restore degraded grasslands and to improve their carbon (C) sequestration. However, the C dynamics and related controlling factors in grasslands with GE have not been well characterized. This synthesis examines the dynamics of soil C content and vegetation biomass with the recovery age through synthesizing results of 51 sites in grasslands in China. The results illustrate increases in soil C content and vegetation biomass with GE at most sites. Generally, both soil C content and vegetation biomass arrive at steady state after 15 years of GE. In comparison, the rates of increase in above- and belowground biomass declined exponentially with the age of GE, whereas soil C content declined in a milder (linear) way, implying a lagged response of soil C to the inputs from plant biomass. Mean annual precipitation ( MAP) and the rate of soil nitrogen (N) change were the main factors affecting the rate of soil C content change. MAP played a major role at the early stage, whereas the rate of soil N change was the major contributor at the middle and late stages. Our results imply that the national grassland restoration projects in China may be more beneficial for C sequestration in humid regions with high MAP. In addition, increased soil N supply to grasslands with GE at the latter recovery stage may enhance ecosystem C sequestration capacity. [ABSTRACT FROM AUTHOR]

Background and aims: Forest fine roots contribute substantially to carbon cycling, and old growth forests have an important role in the global carbon budget. We, hence, studied temporal variation in fine root production and turnover in an old forest. Methods: Fine root dynamics were investigated, using sequential soil cores for 6 years, and related to rainfall and air temperature in a mixed mature broad-leaved Pinus koraiensis forest in northeastern China. Results: The mass, production, mortality, and disappearance of fine roots showed intra-annual variation. Monthly live and dead fine root mass were significantly positively correlated with meteorological conditions of the previous month. Monthly fine root production was associated with air temperature of the current month. The intra-annual pattern of fine root production was similar to that of net primary production and opposite to that of leaf litterfall. Total fine root production accounted for 25 % of net primary production, and the fine root input to soil carbon was 1.2 times larger than the leaf litterfall. Conclusions: Our results indicate tight linkages between fine roots and meteorological conditions. The important role of fine roots in forest carbon budget suggests that forest carbon flux estimations need to take fine root dynamics into account. [ABSTRACT FROM AUTHOR]

The carbon feedback between soil and climate is partly determined by topsoil organic carbon turnover time (τ). However, the τ under future warmer climate still remains unclear. Herein, a manipulative experiment was conducted in a semi-arid grassland on the Loess Plateau of China to investigate the underlying mechanisms of the response of topsoil τ to warming. The results showed that warming significantly increased topsoil τ, which was directly regulated by the decreased temperature sensitivity of soil microbial respiration and indirectly due to the decreased pH and the increased aboveground biomass, soil inorganic nitrogen and soil carbon substrate quality. These results implied that short-term warming could potentially promote soil carbon sequestration in the semi-arid grassland. • Short-term warming did not change top soil organic carbon (SOC) pool. • Short-term warming slowed down SOC turnover. • Short-term warming could potentially promote SOC sequestration in the semi-arid grassland. [ABSTRACT FROM AUTHOR]

• Mean annual temperature was the most critical driver for forest soil carbon. • The northern fir forest had the highest quantity of soil organic and total carbon. • The southern forests had the higher quantity of soil inorganic carbon. • Well- functioning forest ecosystem (SR > 2) over North-South transect. • C sequestration was maximized in temperate zone through fir or broad-leaved forests. The forest ecosystem plays a key role in mitigating global climate change through carbon sequestration in its biomass and soils to limit the rising atmospheric concentration of CO 2. However, the combined overall interaction of climate and forest type on the quantities and forms of soil carbon (organic vs. inorganic) has not yet been sufficiently investigated. In this study, the contents of soil total carbon (STC), soil organic carbon (SOC) and soil inorganic carbon (SIC) were measured along the 4000 km North-South Transect of Eastern China. We sampled 252 soil samples (6 replicates for each site, 3 depths for each site) from four long-term ecosystem experimental stations in Dinghushan, Shennongjia, Beijing and Changbaishan, along the transect from south to north, including 14 different forest types. The contents of STC, SOC, and SIC in the upper 60 cm soil layer varied in different types of forest with 34–107 g C kg−1, 31–104 g C kg−1, and 1.5–8 g C kg−1, respectively. The northern fir and birch forest, most notably in Changbaishan, had the highest STC and SOC contents. The higher SIC contents were found in the southern evergreen broad-leaved forests in Dinghushan and Shennongjia. The contents of STC, SOC and SIC differed significantly in terms of mean annual temperature (MAT), mean annual precipitation (MAP), forest type, and soil depth. In the upper 60 cm soil layer, the most significant correlations occurred between SOC (or STC) and MAT (R2 SOC = −0.62, R2 STC = −0.60) when compared with the correlation between SOC (or STC) and MAP (R2 SOC = −0.45, R2 STC = −0.45) or elevation (R2 SOC = 0.48, R2 STC = 0.48). The soil stratification ratio (SR) of STC and SOC were typically ∼2–3 in most forests and even reached 5– 7 in Changbaishan forest, indicating a well-functioning ecosystem overall. We concluded that on the near-continental scale (4000 km), forest soil carbon contents and forms (SOC, STC, SIC) were controlled most strongly by temperature (MAT). Therefore, an innovative selection of a specific forest type (fir or broad-leaved forest) within set temperature regimes can better contribute to maximizing soil carbon content and thus optimize its sequestration on the national to near-continental scale to mitigate climate change. [ABSTRACT FROM AUTHOR]

Soil carbon (C) in three Ginkgo (Ginkgo biloba L.) agroforestry systems, afforestation (Ginkgo alone; G), and an agricultural cropping system were compared over a five-year period. The agroforestry systems were Ginkgo + Wheat (Triticum aestivum L.) + Peanut (Arachis hypogaea L.; GWP); Ginkgo + Mulberry (Morus alba L.; GM); and Ginkgo + Rapa (Brassica napus L.) + Peanut (GRP). The agricultural system consisted of wheat and peanut (WP). Total soil carbon (TSC), soil organic (SOC) and inorganic carbon (SIC), and the pools of five SOC chemical fractions were measured. TSC and SOC were always lower under WP than the G-based planting systems, and TSC in the latter increased significantly across years in the top 20 cm. Stocks of SIC under WP were significantly greater than the G-based systems, whereas SOC fractions tended to be lower. Most fractions increased across years but not in WP. [ABSTRACT FROM AUTHOR]

Elevated nitrogen (N) deposition has the potential to increase litter and soil carbon (C) storage by suppressing lignolytic activity, but reports of the response of forest floor and soil have shown inconsistent responses. We investigated organic carbon and nitrogen as well as lignin phenols and substituted fatty acids (SFA) in forest floor litter and organic horizons, and mineral soil profiles from a mixed broad-leaf Korean pine ( Pinus koraiensis ) forest, China after 6 years of N addition treatment at double the current N deposition rate. Total C and N were not influenced by experimental N deposition. However, incipient changes in extractable lignin phenol concentration were seen for degraded litter ( P = 0.100) exhibiting increases of about 5% while mineral soil, surface litter and O-horizon showed no change. The degree of lignin oxidation was not substantially influenced in any layer although a significant decrease in vanillyl lignin phenol oxidation was measured in the degraded litter under elevated N. Extractable substituted fatty acids in the forest floor and mineral soil horizons were also, essentially, insensitive to N addition with the minor exception of the O-horizon showing a small but significant (∼16%, P = 0.041) increase. Our results are consistent with one group of literature showing little change in overall soil and litter character under short term, 5–10 years, of N addition. Minor changes in molecular C dynamics, such as those observed for lignin phenols and substituted fatty acids could possibly be attributed to the suppression of microbial decay under N addition. [ABSTRACT FROM AUTHOR]

Afforestation is an effective method to increase carbon (C) sinks and address climate change. It is crucial to understand how the stand growth affects C sequestration capacity, especially when the trade-offs with timber production from plantations have not been fully examined. We used a chronosequence approach to estimate C storage in Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) plantations (including the trees, understory, litter, and soils) at seven stand ages (3, 8–11, 16, 21, 25, 29, and 32 years). Ecosystem C storage increased nonlinearly from 76.4 to 282.2 t ha−1 with stand age and was fitted with a logistic model that had a maximum C storage and age of 271.9 t ha−1 and 33 years, respectively, to reach 95% of the maximum stored C. The C increment was mainly contributed by an increase in tree biomass, which ranged from 2.8 to 177.7 t ha−1 and comprised 4–64% of the total ecosystem C. Live root C (sum of the stump, coarse, and fine root C) showed a logistic increase from 2.0 to 26.3 t ha−1 with stand age and constituted 2.5–9.3% of ecosystem C. Understory plants and litter represented a small pool (<2% of ecosystem C). The C storage in shrubs and litter slightly increased, while that in herbs decreased as the stands aged. Soil C storage was an important and relatively stable pool, ranging from 69.6 to 130.1 t ha−1. Stand volume was also best fitted with a logistic model with a maximum value of 552.6 m3 ha−1. Additionally, the time needed to reach 95% of the maximum volume was 25 years. Hence, extending the rotation age to over 30 years for Chinese fir plantations could potentially maximize the synergistic benefits of C storage to mitigate climate change and obtain timber products for economic profit. [Display omitted] • Chinese fir plantations have high carbon (C) sequestration capacity. • Accumulation of ecosystem C was mainly contributed by increase in tree biomass C. • Soil C storage remained relatively stable except for stand at age of 21 years. • Rotation extension enhances ecosystem C storage and large-trees' timber production. [ABSTRACT FROM AUTHOR]

The establishment of either forest or grassland on degraded cropland has been proposed as an effective method for climate change mitigation because these land use types can increase soil carbon (C) stocks. This paper synthesized 135 recent publications (844 observations at 181 sites) focused on the conversion from cropland to grassland, shrubland or forest in China, better known as the 'Grain-for-Green' Program to determine which factors were driving changes to soil organic carbon ( SOC). The results strongly indicate a positive impact of cropland conversion on soil C stocks. The temporal pattern for soil C stock changes in the 0-100 cm soil layer showed an initial decrease in soil C during the early stage (<5 years), and then an increase to net C gains (>5 years) coincident with vegetation restoration. The rates of soil C change were higher in the surface profile (0-20 cm) than in deeper soil (20-100 cm). Cropland converted to forest (arbor) had the additional benefit of a slower but more persistent C sequestration capacity than shrubland or grassland. Tree species played a significant role in determining the rate of change in soil C stocks (conifer < broadleaf, evergreen < deciduous forests). Restoration age was the main factor, not temperature and precipitation, affecting soil C stock change after cropland conversion with higher initial soil C stock sites having a negative effect on soil C accumulation. Soil C sequestration significantly increased with restoration age over the long-term, and therefore, the large scale of land-use change under the 'Grain-for-Green' Program will significantly increase China's C stocks. [ABSTRACT FROM AUTHOR]

Little is known about the effects of nitrogen (N) additions on soil respiration (Rs) in tropical and subtropical forests. We therefore conducted an N-fertilization experiment in a subtropical evergreen forest in eastern China to better understand the short-term response of Rs to increased N availability. N additions stimulated Rs compared to control plots, yet the magnitude of the increase depended on the amount of N added, with Rs being greater in the low-N treatment (50 kg N ha−1 yr−1) than the high-N treatment (100 kg N ha−1 yr−1). Differences in Rs among treatments correlated with changes in fine root biomass, suggesting increases in Rs reflect those in autotrophic respiration. Our findings challenge the dogma that N fertilization often reduces soil respiration and highlights the need to better understand the effects of low N additions, so as to reliably predict how projected climate change scenarios may affect the cycling of soil carbon (C) in tropical and subtropical forests. [ABSTRACT FROM AUTHOR]

• Context: A large area of abandoned land in the semiarid temperate region of China has been converted into plantations over the past decades. However, little information is available about the ecosystem C storage in different plantations. • Aim and methods: Our objective was to estimate the C storage in biomass, litter, and soil of four different plantations (monospecific stands of Larix gmelinii, Pinus tabuliformis, Picea crassifolia, and Populus simonii). Tree component biomass was estimated using allometric equations. The biomasses of understory vegetation and litter were determined by harvesting all the components. C fractions of plant, litter, and soil were measured. • Results: The ecosystem C storage were as follows: Picea crassifolia (469 t C/ha) > Larix gmelinii (375 t C/ha), Populus simonii (330 t C/ha) > Pinus tabuliformis (281 t C/ha) ( P < 0.05), 59.5-91.1 % of which was in the soil. The highest tree and understory C storage were found in the plantation of Pinus tabuliformis (247 t/ha) and Larix gmelinii (1.2 t/ha) respectively. The difference in tree C fraction was significant among tree components ( P < 0.05), following the order: leaf > branch > trunk > root. The highest soil C (SC) was stored in Picea crassifolia plantation (411 t C/ha), while Populus simonii plantation had a higher SC sequestration rate than others. • Conclusion: C storage and distribution varied among different plantation ecosystems. Coniferous forests had a higher live biomass and litter C storage. Broadleaf forests had considerable SC sequestration potential after 40 years establishment. [ABSTRACT FROM AUTHOR]

Abstract: Subalpine forests in southwestern China were exploited extensively in the second half of the 20th century. Old growth forests (OGFs) dominated by firs had largely been replaced by spruce plantation forests (SPFs), spruce and birch mixed forests (SBMs), natural birch forests (NBFs), and fir and birch mixed forests (FBM). The main objectives of this study are to quantify the ecosystem carbon (C) stock in these five forest types and to estimate their C sequestration capacity. Sixty-nine stands were sampled across the Miyaluo forest region located in the subalpine zone of southwestern China. The C stocks in the tree-layer, understory, herbs, mosses, forest floor, coarse woody debris (CWD) and soil were estimated. The mean total biomass in SPF, SBM, NBF, FBM, and OGF was 125.9, 131.2, 135.7, 191.7, and 651.1t/ha, respectively. The OGF had the highest level of C stock. Total biomass and C density were significantly higher in FBM than those in SPF, SBM and NBF. FBM had a significantly higher mean annual increment (MAI) than all other types. Soil C accounted for a large proportion (68.4–76.5%) of the ecosystem C pools in SPF, SBM, NBF and FBM, but only 40.5% C was stored in the OGF’s soils relative to 51.5% in the biomass. Of the C stock in the upper 0–80cm soil, about 50% was stored in the upper 0–20cm, and more than 74% in the upper 0–40cm. Soil C stock in OGF, NBF and FBM was significantly higher than that in SPF and SBM. Soil disturbance during timber harvest, site preparation and tree planting explains less soil C stock in the SPF and SBM stands compared to other forest types. These results suggest natural mixed forest restoration can be a promising approach for increasing C sequestration capacity in the subalpine region. Also, reducing soil disturbance during forest management practices plays an important role in increasing the soil C stock. [Copyright &y& Elsevier]

Abstract: Indigenous broadleaf plantations are increasingly being developed as a prospective silvicultural approach for substituting coniferous plantations in subtropical China. Three plantations of monoculture and mixed Pinus massoniana and Castanopsis hystrix were selected to examine soil organic carbon (SOC) stocks and temporal and spatial patterns of the main greenhouse gases fluxes for understanding the effects of mixed forests on soil carbon and nitrogen (N) cycling processes. We found that SOC stock in 0–20cm layer in the mixed plantation was 14.3% higher than that in the P. massoniana, and 8.1% higher than that in the C. hystrix plantations. Differences in SOC stock among the plantations were attributed to soil N stock and leaf litterfall input. Soil CO2 and N2O fluxes in the mixed plantation displayed the seasonal trends, while soil CH4 flux did not show the seasonal trend. The seasonal variations in soil CO2 and N2O emissions were positively related to soil temperature and moisture. Mean soil CO2 and N2O emissions (53.2mgCm−2 h−1 and 5.21μgNm−2 h−1, respectively) were significantly higher in the mixed plantation than in the P. massoniana plantation, while they were lower than in the C. hystrix plantation. Mean soil CH4 uptake (38.4μgCm−2 h−1) was significantly higher in the mixed plantation than in the C. hystrix plantation, while it is similar to that in the P. massoniana plantation. Variations in soil CO2 flux among the plantations were influenced by fine root biomass, leaf litterfall mass, soil N stock and soil C:N ratio. Differences in soil N2O flux among the plantations could be attributed to the differences in soil N stock, soil NO3 −−N content and soil C:N ratio. Soil respiration rate and soil NO3 flux among the plantations. This study confirms that the mixed plantation has a higher SOC stock than the monoculture plantations, and there is an increase in amount of GHG absorbed by the soil of mixed plantations compared to C. hystrix plantations. Therefore, a mixture of C. hystrix versus P. massoniana, could be a better silvicultural approach for SOC sequestration than monoculture C. hystrix plantation for substituting P. massoniana plantations in subtropical China. [Copyright &y& Elsevier]−−N content could account for variations in soil CH4 flux among the plantations. This study confirms that the mixed plantation has a higher SOC stock than the monoculture plantations, and there is an increase in amount of GHG absorbed by the soil of mixed plantations compared to C. hystrix plantations. Therefore, a mixture of C. hystrix versus P. massoniana, could be a better silvicultural approach for SOC sequestration than monoculture C. hystrix plantation for substituting P. massoniana plantations in subtropical China. [Copyright &y& Elsevier]