SOC Pool Research Articles

Vegetation redistribution is predicted to intensify soil organic carbon loss under future climate changes on the Tibetan Plateau

Vegetation redistribution may bring unexpected climate-soil carbon cycling in terrestrial biomes. However, whether and how vegetation redistribution alters the soil carbon pool under climate change is still poorly understood on the Tibetan Plateau. Here, we applied the G-Range model to simulate the cover of herbs, shrubs and trees, net primary productivity (NPP) and soil organic carbon density (SOCD) at the depth of 60 cm on Tibetan Plateau for the individual years 2020 and 2060, using climate projection for Representative Concentration Pathways (RCP) 4.5 and RCP8.5 scenarios with the RegCM4.6 model system. Vegetation redistribution was defined as the transitions in bare ground, herbs, shrubs and trees between 2020 and 2060, with approximately 57.9 % (RCP4.5) and 59 % (RCP8.5) of the area will redistribute vegetation over the whole Tibetan Plateau. The vegetation cover will increase by about 2.4 % (RCP4.5) and 1.9 % (RCP8.5), while the NPP and SOCD will decrease by about −14.3 g C m−2 yr−1 and −907 g C m−2 (RCP4.5), and −1.8 g C m−2 yr−1and −920 g C m−2 (RCP8.5). Shrubs and trees will expand in the east, and herbs will expand in the northwest part of the Plateau. These areas are projected to be hotspots with greater SOCD reduction in response to future climate change, and will include lower net plant carbon input due to the negative NPP. Our study indicates that the SOC pool will become a carbon source under increased air temperature and rainfall on the Tibetan Plateau by 2060, especially for the area with vegetation redistribution. These results revealed the potential risk of vegetation redistribution under climate change in alpine ecosystems, indicating the policymakers need to pay attention on the vegetation redistribution to mitigate the soil carbon emission and achieve the goal of carbon neutrality on the Tibetan Plateau.

Long-term vegetation restoration promotes lignin phenol preservation and microbial anabolism in forest plantations: Implications for soil organic carbon dynamics

Vegetation restoration contributes to soil organic carbon (C; SOC) sequestration through the accumulation of plant and microbial residues, but the mechanisms underlying this microbially mediated process are not well resolved. To depict the dynamics of plant- and microbial-derived C in restored forest ecosystems, soil samples were collected from Robinia pseudoacacia plantations of different stand ages (15, 25, 35, 45 years old) established on degraded wheat fields. The results showed that the degree of lignin phenol oxidation decreased with increasing stand age (P < 0.05), and hemicellulose-degrading genes were detected at higher relative abundances than other functional gene categories, indicating selective preservation of recalcitrant lignin phenols. Despite both glucosamine (R2 = 0.61, P < 0.001) and muramic acid (R2 = 0.37, P < 0.001) contents trending upward over time, fungal residual C accounted for a greater proportion of SOC compared with bacterial residual C. Accordingly, fungal residual C, which exhibited a similar response pattern as total microbial residual C to vegetation restoration, was considered a major contributor to the SOC pool. These results provided evidence that long-term vegetation restoration enhanced SOC sequestration in R. pseudoacacia forest by promoting the preservation of plant-derived lignin phenols and concomitant microbial anabolism. Partial least squares-discriminant analysis identified two important ecological clusters (i.e., modules) in the fungal network that profoundly influenced lignin phenol oxidation (P < 0.05) and microbial residual C accumulation (P < 0.01). Among the dominant taxa in microbial networks, the bacterial phyla Proteobacteria and Acidobacteriota had potential to degrade recalcitrant C compounds (e.g., cellulose, lignin), whereas the fungal phylum Ascomycota could outcompete for labile C fractions (e.g., dissolved organic C). Findings of this study can enable a mechanistic understanding of SOC stability driven by microbial turnover in restored forest ecosystems.

Carbon pool and respiration of rhizosphere soils of different mangrove plant species in bangladesh sundarbans

Bangladesh Sundarbans like other mangrove ecosystems are vital carbon reservoirs in the global carbon cycle. Soil respiration, a key carbon flux, is closely linked to climate change. Despite extensive research on the Sundarbans, a gap exists in studying rhizosphere soil carbon pool (SOC) and respiration (Rs), which is crucial for understanding its role in global climate dynamics, especially the local climate. This study investigated SOC pools and Rs rates of oligohaline, mesohaline, and polyhaline zones of the Bangladesh Sundarban Mangrove Forests (SMF). The oligohaline zone exhibited the highest average SOC content (11.26 ± 5.52 t/ha), followed by the mesohaline zone (9.91 ± 3.09 t/ha) and the polyhaline zone (9.86 ± 4.16 t/ha). The Rs rate was comparatively higher in the mesohaline zone (28.19 ± 5.02 mg CO2/g soil), followed by the polyhaline zone (27.81 ± 4.38 mg CO2/g soil), and the oligohaline zone (27.63 ± 4.16 mg CO2/g soil) though the differences were not significant. Further analyses explored the influences of plant species on SOC and Rs. While rhizosphere soil of distinct plant species displayed varying SOC values, Rs did not exhibit significant differences among different plant species, and no significant relation was observed between Rs and SOC values. Mangroves were noted to store substantial amounts of organic carbon in their soils, yet they released relatively less carbon dioxide (CO2) through soil respiration compared to other tropical forests. This unique characteristic underscores the critical role of mangroves in global climate change dynamics. Conclusively, this study offers insightful information about the carbon dynamics of the Bangladesh SMF, emphasizing the significance of mangroves as carbon reservoirs with the potential to influence climate change adaptation strategies. Bangladesh J. Bot. 53(1): 131-140, 2024 (March)

Effect of Vegetation Restoration on Soil Organic Carbon Storage in Coal Mining Areas Based on Meta-analysis

Coal mining is the world's primary means of coping with an increasing energy demand. However, with the mining of coal, the regional ecosystem has been damaged to varying degrees, resulting in a decrease in the "carbon sink" capacity. Vegetation restoration is the basis for the restoration of degraded ecosystems and carbon sequestration functions in mining areas. However, no systematic studies have been conducted on the effects of vegetation restoration on soil organic carbon in coal mining areas on a global scale. Therefore, it is not possible to accurately predict the response of the global SOC pool to vegetation restoration. In this study, soil physicochemical properties of vegetation restoration were collected from 112 peer-reviewed articles to assess the effects of vegetation restoration type, soil depth, restoration year, mean annual temperature, annual precipitation, and elevation on soil organic carbon in coal mining areas and to identify relevant key drivers. The results showed that the damaged coal mine area could significantly improve the physicochemical properties of the soil through vegetation restoration. The restored soils had 39.02% higher SOC reserves compared to that in unrestored or naturally restored soils. When environmental factors were not considered, the vegetation restoration types that were favorable for SOC stock accumulation were cropland > woodland > grassland > shrubland. All four types of vegetation restoration significantly increased the SOC storage in the surface layer (0-20 cm). Grassland and shrubs significantly increased SOC storage at depth (>40 cm), whereas SOC storage at depth under woodland and farmland types was not significantly different from SOC storage after unrestored or natural restoration. The increasing trend of SOC storage after vegetation restoration decreased with increasing soil depth. The specific vegetation restoration strategy should select the appropriate vegetation type according to the climatic conditions. The types of vegetation restoration with higher carbon sequestration effects in damaged coal mining areas with mean annual temperature <0℃ and mean annual precipitation <500 mm were grassland or shrubland. In contrast, woodland and cropland restoration types could better increase SOC storage in environments with mean annual temperature >15℃ and annual precipitation >800 mm. TN, BD, AN, and AK were the main factors influencing the ability to affect soil carbon sequestration. This study can provide a theoretical reference for quantifying the carbon sequestration effects of different vegetation restoration measures in damaged coal mining areas and the restoration and reconstruction of degraded ecosystems.

Interguild fungal competition in litter and soil inversely modulate microbial necromass accumulation during Loess Plateau forest succession

Microbial interactions determine ecosystem carbon (C) and nutrient cycling, yet it remains unclear how interguild fungal interactions modulate microbial residue contribution to soil C pools (SOC) during forest succession. Here, we present a region-wide investigation of the relative dominance of saprophytic versus symbiotic fungi in litter and soil compartments, exploring their linkages to soil microbial residue pools and potential drivers along a chronosequence of secondary Chinese pine (Pinus tabulaeformis) forests on the Loess Plateau. Despite minor changes in C and nitrogen (N) stocks in the litter or soil layers across successional stages, we found significantly lower soil phosphorus (P) stocks, higher ratios of soil C: N, soil N: P and soil C: P but lower ratios of litter C: N and litter C: P in old (>75 years) than young stands (<30 years). Pine stand development altered the saprotroph: symbiotroph ratios of fungal communities to favor the soil symbiotrophs versus the litter saprotrophs. The dominance of saprotrophs in litter is positively related to microbial necromass contribution to SOC, which is negatively related to the dominance of symbiotrophs in soils. Antagonistic interguild fungal competition in litter and soil layers, in conjunction with increased fungal but decreased bacterial necromass contribution to SOC, jointly contribute to unchanged total necromass contribution to SOC with stand development. The saprotroph: symbiotroph ratios in litter and soil layers are mainly driven by soil P stocks and stand parameters (e.g., stand age and slope), respectively, while substrate stoichiometries primarily regulate microbial necromass accumulation and fungal: bacterial necromass ratios. These results provide novel insights into how microbial interactions at local spatial scales modulate temporal changes in SOC pools, with management implications for mitigating regional land degradation.

Straw and phosphorus applications promote maize (Zea mays L.) growth in saline soil through changing soil carbon and phosphorus fractions.

Straw return has been widely recognized as an important carbon (C) enhancement measure in agroecosystems, but the C-phosphorus (P) interactions and their effects on plants in saline soils are still unclear. In this study, we investigated the effects of straw return and three P application levels, no P fertilizer (Non-P), a conventional application rate of P fertilizer (CP), and a high application rate of P fertilizer (HP), on maize growth and soil C and P fractions through a pot experiment. The results revealed that the dry matter weight of maize plant was no difference between the two straw return levels and was 15.36% higher under HP treatments than under Non-P treatments. Plant nutrient accumulations were enhanced by straw addition and increased with increasing P application rate. Straw application reduced the activities of peroxidase (POD), superoxide dismutase (SOD), catalase, and the content of malondialdehyde (MDA) in maize plants by 31.69%, 38.99%, 45.96% and 27.04%, respectively. P application decreased SOD, POD activities and MDA content in the absence of straw. The contents of easily oxidized organic carbon (EOC), particulate organic carbon (POC) and the ratio of POC/SOC in straw-added soils were 10.23%, 17.00% and 7.27% higher, respectively, than those in straw-absent soils. Compared with Non-P treatments, HP treatments led to an increase of 12.05%, 23.04% in EOC, POC contents respectively, while a decrease of 18.12% in the contribution of MAOC to the SOC pool. Straw return improved the P status of the saline soil by increasing soil available P (14.80%), organic P (35.91%) and Ca2-P contents (4.68%). The structural equation model showed that straw and P applications could promote maize growth (indicated by dry matter weight, P accumulation, antioxidant enzyme activity and MDA content) through improving soil C and P availabilities. This study provides evidence that straw return together with adequate P supply in saline soil can promote crop nutrient accumulation, attenuate the oxidation damage on crop growth, and be beneficial for SOC turnover and soil P activation.

Effects of Experimental Nitrogen Deposition and Litter Manipulation on Soil Organic Components and Enzyme Activity of Latosol in Tropical Rubber Plantations

It is of great scientific significance in regulating plantation ecosystem restoration to investigate the effects of the nitrogen (N) deposition and litter manipulation on soil organic carbon components and enzyme activities. A micro-plot experiment was conducted with four nitrogen additions[CK (0 kg·hm-2·a-1, calculated by N), LN (50 kg·hm-2·a-1), MN (100 kg·hm-2·a-1), and HN (200 kg·hm-2·a-1)] and two litter treatments[LR (litter removal) and L (litter retained)] for tropical rubber plantations in western Hainan Island. The soil physico-chemical properties, soil organic carbon components, and enzyme activities in 0-10 cm and 10-20 cm depths were analyzed. The results showed that soil pH significantly decreased with elevated N addition and litter removal. The contents of NO3--N and NH4+-N significantly increased with elevated N addition. Moreover, there was a significant interaction between N addition and litter treatment on the contents of NO3--N and NH4+-N (P &lt; 0.05). Compared to that with L, LR reduced SOC and its component contents; particularly, the largest decrease was in LFOC by 29.0%-81.4% in the 0-10 cm depth and 23.5%-58.4% in 10-20 cm, respectively. The contents of SOC and its components presented a trend of increasing first and then decreasing with elevated N addition irrespective of litter treatment, and those contents were significantly higher at LN than those at HN. There was a significant interaction between N addition and litter treatment on SOC, LFOC (0-10 cm), and HFOC contents. Compared with that under L, PPO activity was significantly reduced at LR under CK and LN but was significantly increased at LR under MN and HN, respectively. Variance analysis showed significant interactive effects between N addition and litter treatment on PPO and CBH (0-10 cm) activities, and the soil enzyme activity (BG, PPO, and CBH) responding to N addition was greater than that to the litter treatment. Pearson correlation analysis showed that SOC content was extremely positively correlated with MBC, POC, LFOC, and HFOC contents. To summarize, litter retained combined with low N deposition played an important synergistic role of improving SOC pool and soil enzyme activities for tropical rubber plantation systems.

Conservation agriculture's impact on total and labile organic carbon pools in calcareous and non-calcareous floodplain soils under a sub-tropical rice-based system.

To evaluate the effects of conservation agriculture (CA) on SOC pools and their lability, field experiments (2015-2020) were conducted on contrasting soils under subtropical climates. The experiment on non-calcareous soils, was comprised of tillage (minimum [MT] vs. conventional [CT]) in main plots, cropping systems (Wheat [Triticum aestivum]-Aus and Aman rice [Oryza sativa L.], WRR; Lentil [Lens culinaris]-Aus and Aman rice, LRR; and Mustard [Brassica nigra]- Boro and Aman rice, MRR) in the sub-plots, and crop residue (with or without 20% residue) in the sub-sub plots. The experiment on calcareous soils, was comprised of tillage (strip-till, ST; no-till, NT; and CT) and crop residue (high residue, HR at 50% by height vs. low residue, LR at 15%). Results showed that the MT had higher SOC contents by 18.8% than the CT in non-calcareous soils. Likewise, SOC was 12.5% and 6.7% higher in the NT and ST, respectively, than in the CT in calcareous soils. Significantly higher particulate organic (POC), permanganate oxidizable (POXC), and microbial biomass carbon (MBC) were observed in the MT, NT, and ST than in the CT at both locations. Reduced tillage with residue retention under LRR had a higher SOC, including labile C pools compared to WRR and MRR systems. Similarly, carbon management index (1.2-1.5 and 1.0-1.2) in both soils had significant positive correlations with SOC lability via POXC, POC, and MBC pools, indicating a SOC sequestration potential. In conclusion, our results showed positive effects of CA on SOC and its lability across soils.

Rehabilitative capacity of amendments to restore maize productivity following artificial topsoil erosion/ deposition

Anthropogenic activities leading to erosion-induced topsoil loss still present a pertinent threat to maize (Zea mays L.) productivity across the U.S. Corn Belt region. Using soil amendments has been proven effective in reversing the effects caused by erosion-induced topsoil loss and restoring agronomic productivity and yields to pre-eroded conditions. The current study investigated the impact of simulated erosion and repeated amendment application on agronomic productivity and yields over five growing seasons for a 23-year-old experiment at two central Ohio sites (Waterman Farm: WF; Western Station: WS). Simulated erosion/deposition was employed in 1997 to create three incremental topsoil depths (TSD) (20 cm topsoil removed (TSD-0); 0 cm topsoil removed (TSD-1); 20 cm topsoil added (TSD-2). Three soil amendments (inorganic, synthetic N fertilizer (INO); organic, compost manure (MAN); no amendment (CON)) were investigated for their ability to restore productivity in these cropping systems. Greater TSD produced higher germination counts and crop stand and yielded greater canopy cover during the initial five weeks after germination. The MAN amended soils observed higher values for the productivity parameters during the 2016–2020 growing seasons. Grain and biomass yields were 34–51% and 5–12% lower, respectively, for the TSD-0 level and 4–10% and 3–6% greater, respectively, for the TSD-2 level when compared to the undisturbed, TSD-1 level. Relative biomass yield losses (% per cm topsoil depth lost) were 0.921 for the WF site and 0.254 for the WS site, corresponding to average biomass losses (Mg ha−1 cm−1 yr−1) of 0.083 and 0.026 for each site. Relative grain yield losses (% per cm topsoil depth lost) were 1.29 for the WF site and 0.514 for the WS site, equating to mean grain losses (Mg ha−1 cm−1 yr−1) of 0.083 and 0.026 for each site. The rehabilitative capacity of the soil amendments followed a trend of INO > MAN at the WF site and MAN > INO > CON at the WS site. The deleterious effects of erosion on grain and biomass yields were found to be reversed with the addition of the INO and MAN amendments at the WS site due to improvements in soil health and SOC pools. The MAN amended soils produced grain and biomass yields that were nearly 2.5% and 5.6% greater than the INO amended soil when compared to the reference treatment (TSD-1-CON). This study demonstrates that sustainable soil management practices coupled with annual soil amendment addition can mitigate the deleterious effects of erosion and rebound maize yields to pre-eroded conditions for soils experiencing severe topsoil loss.

Effect of land use and soil depth on the distribution of phyto-available nutrients and SOC pools of Vertisols in Central India.

A proper understanding of soil parameters under different production systems of the world is necessary for efficient soil management. We, therefore, carried out the present study to assess the status of some selected soil properties (soil pH and electrical conductivity (EC)), phyto-available nutrients (available nitrogen (AN), available potassium (AK), exchangeable calcium (Ex. Ca), exchangeable magnesium (Ex. Mg), available sulfur (AS), and soil organic carbon (SOC) pools (SOC, total organic carbon (TOC), very labile C, labile C, less labile C, and non-labile C) and to establish relationships among the measured soil parameters at different depths of Vertisols of India under various land uses. A total of 150 composite soil samples (from 25 plots including nine from agricultural land, nine from horticultural land, three from forest land, and four from grassland) were collected from 6 soil depths viz, 0-10, 10-20, 20-40, 40-60, 60-80, and 80-100 cm under agriculture, horticulture, forest, and grassland land uses present in Central India and analyzed. The values of soil pH, EC, AN, AK, Ex. Ca, Ex. Mg, and AS in various soil depths under different land uses varied widely. The values of SOC (0.19 to 1.00%), TOC (0.58 to 2.42%), very labile C (0.14 to 0.83%), labile C (0.05 to 0.25%), less labile C (0.05 to 0.26%) and non-labile C (0.23 to 1.42%) in various soil depths under different land uses also varied significantly. Forest and grassland land uses had higher levels of SOC, TOC, very labile, and non-labile C content in all the soil depths in comparison to SOC, TOC, very labile, and non-labile C content in different soil depths under agriculture and horticulture land use. The levels of SOC, TOC, very labile, and non-labile C content under all the land uses decreased with increasing soil depths. SOC was positively and significantly correlated with AN, AK, AS, and estimated SOC pools in surface soil layers. Principal component analysis (PCA) of soil parameters in different soil depths resulted in 5 principal components (PCs) with > 1 eigenvalue and accounting for > 75% variability. This information could be used for managing SOC status and phyto-available nutrients in Vertisols under different land uses.

Effects of Straw Returning with Lime on SOC and Carbon Pool Management in Acidic Paddy Soil

Soil acidification and low SOC are the main limiting factors in acidic paddy soils. Straw returning with lime is an effective measure to alleviate soil acidification and improve soil fertility; however, its interaction effects on SOC and carbon pool management are still unclear. To investigate the impact of straw returning with lime on the organic carbon pool of acidic paddy soil, field experiments were conducted on acidic paddy soil in Baiyun District and Huiyang District of Guangdong Province. The changes in soil total organic carbon (TOC), water-soluble organic carbon (DOC), active organic carbon (LOC), particulate organic carbon (POC), microbial biomass carbon (MBC), carbon pool index (CPI), stable organic carbon (IOC), carbon pool activity (L), carbon pool activity index (CPAI), and carbon pool management index (CPMI) were analyzed under three treatments (CK, conventional fertilization; RS, straw returning+conventional fertilization; RS+L straw returning with lime+conventional fertilization). The results demonstrated that compared with that in CK, the TOC, LOC, POC, and MBC in the RS+L treatment were significantly increased by 10.24%-17.79%, 34.49%-44.37%, 19.27%-23.59%, and 33.36%-43.26%, respectively (P<0.05). Compared with that in CK, the RS+L treatment significantly increased the DOC content during the early growth stage (15-45 days after transplanting) of rice (P<0.05) but had no significant influence on the DOC content during the late growth stage of rice. Compared with that in RS, the TOC, LOC, POC, and MBC in the RS+L treatment were increased by 2.15%-6.95%, 1.17%-17.90%, 4.27%-8.65%, and 12.99%-14.53%, respectively. Compared with that in CK, the RS+L treatment significantly increased IOC and CPI by 8.32%-15.57% and 14.00%-20.00%, respectively (P<0.05). Compared with that in the CK treatment, the RS treatment significantly increased CPI by 14.00%-18.00% (P<0.05). No significant differences in L, CPAI, or CPMI were detected among the different treatments. The soil pH in the RS+L treatment was significantly higher than that in the CK treatment (P<0.05). No significant differences in rice yield were detected among the different treatments. Principal component analysis demonstrated that rice yield was primarily correlated with DOC, LOC, CPAI, and CPMI but its contribution to SOC and carbon pool management index was low. Principal component analysis also indicated that straw returning with lime could improve soil pH and nutrient contents of acidic paddy soil, driving the formation and accumulation of organic carbon fraction such as MBC and POC, thus boosting the increase in SOC. In conclusion, straw returning with lime is beneficial to the accumulation of MBC, POC, LOC, and IOC in acidic paddy soil to improve the content and stability of soil total organic carbon, which is an effective way to improve the carbon sequestration of acidic paddy soil.

Biochar application significantly increases soil organic carbon under conservation tillage: an 11-year field experiment

Biochar application and conservation tillage are significant for long-term organic carbon (OC) sequestration in soil and enhancing crop yields, however, their effects on native soil organic carbon (native SOC) without biochar carbon sequestration in situ remain largely unknown. Here, an 11-year field experiment was carried out to examine different biochar application rates (0, 30, 60, and 90 Mg ha−1) on native SOC pools (native labile SOC pool I and II, and native recalcitrant SOC) and microbial activities in calcareous soil across an entire winter wheat–maize rotation. The proportions of C3 and C4-derived native SOC mineralization were quantified using soil basal respiration (SBR) combined with 13C natural isotope abundance measurements. The results showed that 39–51% of the biochar remained in the top 30 cm after 11 years. Biochar application rates significantly increased native SOC and native recalcitrant SOC contents but decreased the proportion of native labile SOC [native labile SOC pool I and II, dissolved organic carbon (DOC), and microbial biomass carbon (MBC)]. Biochar application tended to increase the indicators of microbial activities associated with SOC degradation, such as SBR, fluorescein diacetate hydrolysis activity, and metabolic quotient (qCO2). Meanwhile, higher biochar application rates (B60 and B90) significantly increased the C4-derived CO2 proportion of the SBR and enhanced C4-derived native SOC mineralization. The effect of the biochar application rate on the content and proportion of native SOC fractions occurred in the 0–15 cm layer, however, there were no significant differences at 15–30 cm. Soil depth also significantly increased native labile SOC pool I and II contents and decreased qCO2. In conclusion, the biochar application rate significantly increased native SOC accumulation in calcareous soil by enhancing the proportion of native recalcitrant SOC, and biochar application and soil depth collectively influenced the seasonal turnover of native SOC fractions, which has important implications for long-term agricultural soil organic carbon sequestration.Graphical

Seasonal Biotic Processes Vary the Carbon Turnover by Up To One Order of Magnitude in Wetlands

AbstractSoil Organic Carbon (SOC) turnover τ in wetlands and the corresponding governing processes are still poorly represented in numerical models. τ is a proxy to the carbon storage potential in each SOC pool and C fluxes within the whole ecosystem; however, it has not been comprehensively quantified in wetlands globally. Here, we quantify the turnover time τ of various SOC pools and the governing biotic and abiotic processes in global wetlands using a comprehensively tested process‐based biogeochemical model. Globally, we found that τ ranges between 1 and 1,000 years and is controlled by anaerobic (in 78% of global wetlands area) and aerobic (15%) respiration, and by abiotic destabilization from soil minerals (5%). τ in the remaining 2% of wetlands is controlled by denitrification, sulfur reduction, and leaching below the subsoil. τ can vary by up to one order of magnitude in temperate, continental, and polar regions due to seasonal temperature and can shift from being aerobically controlled to anaerobically controlled. Our findings of seasonal variability in SOC turnover suggest that wetlands are susceptible to climate‐induced shifts in seasonality, thus requiring better accounting of seasonal fluctuations at geographic scales to estimate C exchanges between land and atmosphere.

Response of soil microbial Communities, inorganic and organic soil carbon pools in arid saline soils to alternative land use practices

Soil organic and inorganic carbon (SOC & SIC) and microbial community structure are key indicators of soil quality and productivity in arid-saline soils. Salinity stress and diminishing availability of freshwater (FW) for irrigation are major constraints for productivity and improving soil quality indicators. Using treated wastewater (TW) and implementing climate-smart cropping systems are promising alternatives to replace freshwater usage in intensive cropping systems, however, impacts on the microbial community and net-carbon sequestration potential are not clearly understood. This field study was conducted in an arid saline-soil to investigate soil microbial community structure and soil carbon contents under a combination of treatments comparing bioenergy sorghum (So) and switchgrass (Sg), two irrigation water sources (FW & TW), and gypsum amendment (GA), to a native-soil control. After three years of implementing these treatments, soil samples were collected and analyzed for total carbon (TC), SOC, SIC, microbial biomass-carbon (MBC) and microbial community structure. Results showed that TW increased microbial diversity and shifted the community structure towards copiotroph-dominated prokaryotes. Several predominant and responsive taxa were associated with divergent trends of SOC, SIC and salinity parameters. Both SOC and SIC pools were sensitive to treatments and demonstrated divergent trends, as contents of TC and SOC were higher in TW-treatments, but of SIC were significantly lower in several So_TW treatments. Treatment TW_So_GA assembled a distinctive microbial community structure, accumulated the highest content of SOC (7.66 g kg−1) but recorded the lowest content of SIC (6.63 g kg−1). The lowest content of SOC was observed in native soil (4.58 g kg−1) but contained the highest SIC (8.15 g kg−1). The study results revealed the agronomic systems with higher potential for increasing TC and SOC content in arid-saline soils. Surface soil SIC was responsive to agronomic management, and several treatments produced disparate impacts on SOC and SIC stocks, which warrant for considering TC as the key indicator for assessing carbon sequestration in arid lands.

Complementation between microbial necromass and plant debris governs the long-term build-up of the soil organic carbon pool in conservation agriculture

Plant residue is ultimately the source of soil organic matter but occurs as a continuum from relatively fresh plant tissue to highly evolved components. Nevertheless, the extent to which crop residue accumulates as plant tissue versus microbial necromass in conservation agricultural systems is still uncertain. A 12-year conservation tillage experiment with maize additions of zero, half and full harvest was conducted in Northeast China. Soil samples in the 0–10 cm depth were collected at 1–4 year intervals. The microbial residue biomarker amino sugar and plant component biomarker lignin phenol were quantified to trace the dynamics of microbial necromass and plant debris. Compared with the initial value, the content of amino sugar increased exponentially to 21–45% and approached steady-state equilibrium after 12 years of maize straw mulching, indicating the existence of “microbial carrying capacity” under repeated plant residue addition. With prolonged duration of conservation tillage and increasing rate of maize straw return, the ratio of amino sugar to lignin phenol decreased from 6.2 to 1.7, accompanied by a decreased degree of lignin side-chain oxidation, indicating that organic input enhanced the selective retention of fresh plant lignin to a larger extent than microbial necromass. The build-up of the SOC pool under conservation tillage was critically controlled by the functional complementation of microbial- and plant-derived components. Maize straw input was able to enhance the contribution of microbial necromass to SOC stabilization by increasing fungal necromass accumulation, while the retention of lignin-like plant debris enlarged the SOC pool capacity and potentially maintained the decomposability of SOC in the long term.

Mean annual temperature and carbon availability respectively controlled the contributions of bacterial and fungal residues to organic carbon accumulation in topsoil across China's forests

AbstractAimSoil organic carbon (SOC) stabilization has become an important topic in recent years in the context of global climate change. Microbial residues represent a significant component of stabilized SOC pools. However, spatial variations in the contributions of bacterial and fungal residues to SOC and their determinants at a continental scale remain poorly understood. We aimed to evaluate the spatial variations and controls of the contributions of microbial residues to SOC in forest topsoil.LocationNorth–south transect in eastern China.Time period2014.Major taxa studiedForest ecosystems.MethodsA total of 195 surface (0–10 cm) soils were sampled from 28 forest sites across tropical and boreal forests in eastern China from July to August to assess how biotic and abiotic factors govern the geographic patterns of the contributions of soil microbial residues (indicated by amino sugars) to SOC.ResultsFungal residues (30.0%) had a greater average contribution to SOC than bacterial residues (15.5%). The contributions of bacterial (CBR) and total microbial residues (CMR) to SOC showed negative latitudinal patterns and were positively correlated with mean annual temperature (MAT). In contrast, the contribution of fungal residues to SOC (CFR) showed no clear geographic or climatic patterns. On average, the CBR (9.7%), CFR (21.1%) and CMR (30.8%) were lower in boreal forests than in other biome forests. SOC concentration negatively mediated CBR, CFR and CMR. The piecewise structural equation model results showed that MAT was the primary driver of the geographic pattern of CBR, whereas SOC and soil carbon : nitrogen ratio were more directly associated with the CFR. Additionally, plant factors and microbial properties (i.e., microbial biomass and composition) played relatively little roles in regulating CBR, CFR and CMR.Main conclusionsThese findings advance the current knowledge of the different geographic patterns of CBR and CFR regulated by different potential mechanisms in forest ecosystems. This highlights that the dynamics of microbial residues could potentially have unexpected consequences for topsoil SOC stocks under climate change.

Responses of microbial necromass carbon and microbial community structure to straw- and straw-derived biochar in brown earth soil of Northeast China.

Soil microbial organisms are conducive to SOC sequestration. However, little attention has been given to the contributions of living MBC and microbial necromass carbon to the SOC pool under biochar and straw amendments. The aims of the study were to explore (1) the effects of maize straw and biochar on MBC, POC, MAOC, DOC and microbial necromass carbon; (2) the contribution of MBC and microbial necromass carbon to the SOC pool; and (3) the relationships among the soil microbial community structure, microbial necromass carbon and other SOC fractions under maize straw and biochar application for nine consecutive years. Three treatments were studied: CK (applied chemical fertilizer only), BC (biochar applied annually at a rate of 2.625 t ha−1 combined with chemical fertilizer), and SR (straw applied annually at a rate of 7.5 t ha−1). Both biochar and straw increased the SOC contents after nine successive maize plant seasons; the DOC and MAOC contents were also increased by biochar and straw amendments. Biochar had advantages in increasing POC contents compared to straw. Biochar and straw increased MBC contents by 48.54% and 60.83% compared to CK, respectively. Straw significantly increased the Galn, GluN, MurA, ManN and total amino contents (P < 0.05); however, biochar significantly increased the Galn and GluN contents (P < 0.05) but had no impact on the MurA contents and decreased the ManN contents. Biochar mainly increased the fungal-derived necromass carbon contents but had no effect on the bacterial-derived necromass carbon, and straw increased both the bacterial- and fungal-derived necromass carbon contents. Straw had no influence on the ratios of microbial necromass carbon accounting for SOC and MAOC, but biochar decreased the ratios in the current study. Similarly, biochar mainly increased the fungal PLFA and total PLFA contents compared to CK, but straw increased bacterial PLFAs, fungal PLFAs and Actinomycetes PLFAs. Maize yield were increased by 7.44 and 9.16% by biochar and straw application, respectively. These results indicate that biochar stimulates fungal activities and turnover to contribute to the stable soil carbon pool and that biochar also improves POC contents to improve the soil organic carbon sink.

Conservation tillage facilitated soil carbon sequestration through diversified carbon conversions

The organic carbon content of soil (SOC) is a key factor for soil health and in climate change. Both tillage practice and straw returns influence the SOC pool. However, their comprehensive impacts on SOC sequestration remain largely unknown. We quantified SOC characteristics, including different labile fractions of soil carbons, and chemical compositions of SOC in cropland soil under long-term (1985–2019) wheat-maize rotation with different tillage and straw return practices. No-tillage (NT) increased the plow layer SOC stocks significantly, as compared with the conventional tillage, and both contents of easily oxidizable organic carbon (EOC) and particulate organic carbon (POC) were enlarged by straw return practices. In particular, NT resulted in considerably larger contribution of labile C (O-alkyl C) and recalcitrant C (such as aromatic C) to SOC sequestration than conventional tillage, suggesting that more diversified C conversion was responsible for enhanced SOC sequestration. Additionally, NT decreased the ratio of alkyl C to O-alkyl C as well as the ratio of lignin to polysaccharides (SOC degradation indices), indicating a lower degree of SOC decomposition. The present study offers new insights into the functional roles of long-term NT and straw return practices on SOC turnover, which are crucial for improving agricultural soil quality and carbon management strategies.

Soil Organic Carbon Isotope Tracing in Sorghum under Ambient CO2 and Free-Air CO2 Enrichment (FACE)

As atmospheric carbon dioxide concentrations, [CO2Air], continue their uncontrolled rise, the capacity of soils to accumulate or retain carbon is uncertain. Free-air CO2 enrichment (FACE) experiments have been conducted to better understand the plant, soil and ecosystem response to elevated [CO2], frequently employing commercial CO2 that imparts a distinct isotopic signal to the system for tracing carbon. We conducted a FACE experiment in 1998 and 1999, whereby sorghum (C4 photosynthetic pathway) was grown in four replicates of four treatments using a split-strip plot design: (i) ambient CO2/ample water (365 μmol mol−1, “Control–Wet”), (ii) ambient CO2/water stress (“Control–Dry”), (iii) CO2-enriched (560 μmol mol−1, “FACE–Wet”), and (iv) CO2-enriched/water stressed (“FACE–Dry”). The stable-carbon isotope composition of the added CO2 (in FACE treatments) was close to that of free atmosphere background values, so the subsequent similar 13C-enriched carbon signal photosynthetically fixed by C4 sorghum plants could be used to trace the fate of carbon in both FACE and control treatments. Measurement of soil organic carbon content (SOC (%) = gC/gdry soil × 100%) and δ13C at three depths (0–15, 15–30, and 30–60 cm) were made on soils from the beginning and end of the two experimental growing seasons. A progressive ca. 0.5‰–1.0‰ δ13C increase in the upper soil SOC in all treatments over the course of the experiment indicated common entry of new sorghum carbon into the SOC pools. The 0–15 cm SOC in FACE treatments was 13C-enriched relative to the Control by ca. 1‰, and according to isotopic mass balance, the fraction of the new sorghum-derived SOC in the Control–Wet treatment at the end of the second season was 8.4%, 14.2% in FACE–Wet, 6.5% in Control–Dry, and 14.2% in FACE–Dry. The net SOC enhancement resulting from CO2 enrichment was therefore 5.8% (or 2.9% y−1 of experiment) under ample water and 7.7% (3.8% y−1 of experiment) under limited water, which matches the pattern of greater aboveground biomass increase with elevated [CO2Air] under the Dry treatment, but no parallel isotopic shifts were found in deeper soils. However, these increased fractions of new carbon in SOC at the end of the experiment do not necessarily mean an increase in total SOC content, because gravimetric measurements of SOC did not reveal a significant increase under elevated [CO2Air], at least within the limits of SOC-content error bars. Thus, new carbon gains might be offset by pre-experiment carbon losses. The results demonstrate successful isotopic tracing of carbon from plants to soils in this sorghum FACE experiment showing differences between FACE and Control treatments, which suggest more dynamic cycling of SOC under elevated [CO2Air] than in the Control treatment.

Soil carbon pool and dynamics of different fractions in subalpine temperate coniferous forests of Western Himalaya, India.

Natural forests have the ability to sequester atmospheric carbon for a long time and fix it into the soil through a variety of processes such as decomposition and root respiration. The changing environment of alpine forests alters the characteristics of soil carbon, causing it to be divided into several components. The current study looked at soil carbon fractions and how they changed over time, both annually and seasonally, at different depths and along an altitudinal gradient. Seasonal sampling was carried out at three depths, with standard procedures employed to estimate the results of soil carbon fractions. The results showed that the surface layer (10 cm) had the highest value of all soil qualities such as SOC, Fraction I, Fraction II, Fraction III, SOM and active pool of carbon than the subsurface (20 cm and 30 cm) layers with autumn dominating the seasons. Site 1 had the highest value and Site 4 lowest, indicating that altitudinal variance had a direct relationship with distinct soil fractions. On an annual basis, the corresponding soil carbon fraction variation was examined, revealing the maximum retention capability at 30 cm of depth. According to the findings, the soils of the Western Himalayas have a high potential for carbon sequestration and conversion into various fractions, with significant annual and seasonal change due to changing environmental conditions.