Soil Organic Carbon Decomposition Research Articles

Global pattern of organic carbon pools in forest soils.

Understanding the mechanisms of soil organic carbon (SOC) sequestration in forests is vital to ecosystem carbon budgeting and helps gain insight in the functioning and sustainable management of world forests. An explicit knowledge of the mechanisms driving global SOC sequestration in forests is still lacking because of the complex interplays between climate, soil, and forest type in influencing SOC pool size and stability. Based on a synthesis of 1179 observations from 292 studies across global forests, we quantified the relative importance of climate, soil property, and forest type on total SOC content and the specific contents of physical (particulate vs. mineral-associated SOC) and chemical (labile vs. recalcitrant SOC) pools in upper 10 cm mineral soils, as well as SOC stock in the O horizons. The variability in the total SOC content of the mineral soils was better explained by climate (47%-60%) and soil factors (26%-50%) than by NPP (10%-20%). The total SOC content and contents of particulate (POC) and recalcitrant SOC (ROC) of the mineral soils all decreased with increasing mean annual temperature because SOC decomposition overrides the C replenishment under warmer climate. The content of mineral-associated organic carbon (MAOC) was influenced by temperature, which directly affected microbial activity. Additionally, the presence of clay and iron oxides physically protected SOC by forming MAOC. The SOC stock in the O horizons was larger in the temperate zone and Mediterranean regions than in the boreal and sub/tropical zones. Mixed forests had 64% larger SOC pools than either broadleaf or coniferous forests, because of (i) higher productivity and (ii) litter input from different tree species resulting in diversification of molecular composition of SOC and microbial community. While climate, soil, and forest type jointly determine the formation and stability of SOC, climate predominantly controls the global patterns of SOC pools in forest ecosystems.

Whole-soil warming leads to substantial soil carbon emission in an alpine grassland.

The sensitivity of soil organic carbon (SOC) decomposition in seasonally frozen soils, such as alpine ecosystems, to climate warming is a major uncertainty in global carbon cycling. Here we measure soil CO2 emission during four years (2018-2021) from the whole-soil warming experiment (4 °C for the top 1 m) in an alpine grassland ecosystem. We find that whole-soil warming stimulates total and SOC-derived CO2 efflux by 26% and 37%, respectively, but has a minor effect on root-derived CO2 efflux. Moreover, experimental warming only promotes total soil CO2 efflux by 7-8% on average in the meta-analysis across all grasslands or alpine grasslands globally (none of these experiments were whole-soil warming). We show that whole-soil warming has a much stronger effect on soil carbon emission in the alpine grassland ecosystem than what was reported in previous warming experiments, most of which only heat surface soils.

Low Carbon Loss from Long-Term Manure-Applied Soil during Abrupt Warming Is Realized through Soil and Microbiome Interplay.

Manure application is a global approach for enhancing soil organic carbon (SOC) sequestration. However, the response of SOC decomposition in manure-applied soil to abrupt warming, often occurring during diurnal temperature fluctuations, remains poorly understood. We examined the effects of long-term (23 years) continuous application of manure on SOC chemical composition, soil respiration, and microbial communities under temperature shifts (15 vs 25 °C) in the presence of plant residues. Compared to soil without fertilizer, manure application reduced SOC recalcitrance indexes (i.e., aliphaticity and aromaticity) by 17.45 and 21.77%, and also reduced temperature sensitivity (Q10) of native SOC decomposition, plant residue decomposition, and priming effect by 12.98, 15.98, and 52.83%, respectively. The relative abundances of warm-stimulated chemoheterotrophic bacteria and fungi were lower in the manure-applied soil, whereas those of chemoautotrophic Thaumarchaeota were higher. In addition, the microbial network of the manure-applied soil was more interconnected, with more negative connections with the warm-stimulated taxa than soils without fertilizer or with chemical fertilizer applied. In conclusion, our study demonstrated that the reduced loss of SOC to abrupt warming by manure application arises from C chemistry modification, less warm-stimulated microorganisms, a more complex microbial community, and the higher CO2 intercepting capability by Thaumarchaeota.

Functional type mediates the responses of root litter-driven priming effect and new carbon formation to warming

Input of root litter can alter soil organic carbon (SOC) dynamics via causing priming effect (PE) on native SOC decomposition and forming new SOC. However, it is unknown how functional type mediates the root litter-driven PE and new C formation as well as their response to warming, which are of pivotal for soil C budget. We mixed litter segments of absorptive roots and transport roots from a Chinese fir (Cunninghamia lanceolata) plantation into isotopically distinct soil and incubated at 19°C (local mean annual temperature) and 23°C (warming by 4°C) for 210 days. Cumulative PE was calculated via integrating the instantaneous PE rates during the incubation. And the newly formed root litter-derived SOC (SOCrl) was calculated by measuring the δ13C value of soil at the end of incubation using a two-source mixed model. We found that absorptive roots with faster decomposition rates, caused significantly higher cumulative PE and SOCrl than transport roots. The microbial biomass and enzyme activities involved in C, N and P acquisition were significantly higher in the absorptive- than the transport roots addition treatment, indicating a higher level of microbial activation caused by absorptive roots. Although warming significantly increased the litter decomposition for both of functional types, while just significantly increased the PE of transport roots, indicating a root functional type dependent sensitivity of PE to warming. However, warming had no significant effect on SOCrl either for absorptive roots or for transport roots. As a consequence, warming relatively decreased the net SOC balance (difference between PE and SOCrl) in the transport roots addition treatment. Overall, our study highlights, for the first time, that functional type primarily mediates the response of root litter-driven PE to climate warming but not the new C formation, which may advance our understanding of SOC dynamics in Chinese fir plantation under climate change.

Regulation of soil organic carbon dynamics by microbial communities during reforestation of Chinese fir plantations after clear‐cutting

AbstractReforestation after forest clear‐cutting is an effective measure to increase soil organic carbon (SOC) sequestration; still, the soil C balance under reforestation and the role of microbial communities in that process remain to be determined. Samples of organic (0–2 cm) and mineral (2–10 cm) horizons were collected from the 7‐, 15‐, 20‐, 29‐, and 36‐year‐old forest stands of Chinese fir (Cunninghamia lanceolata) after plantation clear‐cutting in subtropical zone under the condition of phosphorus limitation. Particulate organic carbon (POC), mineral‐associated organic carbon (MAOC), microbial phospholipid fatty acids (PLFAs), and enzymatic activities for C, nitrogen (N), and phosphorus (P) acquisition were analyzed. The lowest contents of POC (10%) and MAOC (13%) in the organic horizon were found in 7‐year‐old stands due to the slow tree regrowth and extensive decomposition of SOC in the first years of forest regrowth. POC (2.0×) and MAOC (0.8×) increases in the organic horizon with forest age were attributed to the stand development and accumulation of above‐ and belowground litter. The organic horizon had a higher POC:MAOC ratio than the mineral (0.7–1.1 vs. 0.2–0.5), indicating lower SOC stability in the first one. The ratio of POC:MAOC increased with the Gram‐positive to Gram‐negative bacteria (G+:G‐) ratio, pointing out that microbial communities developed a specific community structure and substrate utilization strategies of organic matter under plantation restoration. The increase of total PLFAs and the G+:G‐ ratio was closely linked with the microbial C and P limitations, indicating that microorganisms shifted community structure to slow‐growing species and increased their content to cope with the C and P restrictions. In the soils of young plantations, microorganisms were limited by C and P; however, the C limitation was alleviated in the 36‐year‐old plots in the organic horizon due to increased litter input, whereas the P limitation was not. This discrepancy between C and P limitation suppressed the decomposition of litter entering the soil, which was seen in decreased specific activity of C degrading enzymes and led to the accumulation of POC in the organic horizon. Thus, soil C sequestration under reforestation of Chinese fir can be controlled by the amount of litter entering the soil and by metabolic C, N, and P limitations that force microorganisms to shift community structure and change their activity.

Changes in microbial composition explain the contrasting responses of glucose and lignin decomposition to soil acidification in an alpine grassland

Soil acidification often suppresses microbial growth and activities, resulting in a negative impact on soil organic carbon (C) decomposition. While the detrimental effects of acidification on soil and plant properties have been extensively studied, less attention has been paid on the shifts in soil microbial communities and their influences of the decomposition of organic C with different chemical complexities. Taking advantage of an acid addition experiment in a Tibetan alpine meadow, here we examined the response of soil microbial communities to soil acidification and microbial effect on the decomposition of organic C with different chemical complexities (i.e., glucose and lignin, representing labile and recalcitrant C respectively). We found that soil acidification had no impact on microbial respiration and microbial abundance even though it decreased bacterial diversity significantly. Soil acidification increased the relative abundance of some microbial taxa, like Alphaproteobacteria and Acidobacteriia in bacteria increased by 36 %, 284 %, and Eurotiomycetes, Sordariomycetes and Leotiomycetes in fungi increased by 145 %, 279 % and 12.7-fold, but decreased the relative abundance of Acidimicrobiia by 33 % in highest acid addition treatment. Changes in microbial communities (bacterial and fungal community composition, the diversity of bacterial community and the ratio of fungi to bacteria) are significantly related to the decomposition of glucose and lignin. More specifically, soil acidification decreased the decomposition of glucose but increased the decomposition of lignin, indicating a trade-off between the decomposition of labile and recalcitrant soil organic C under soil acidification. Overall, shifts in microbial communities under soil acidification might be accompanied by an increased ability to break down more recalcitrant C. This trade-off between the decomposition of labile and recalcitrant C may change soil C quality under future acid deposition scenarios.

Effects of the combined application of livestock manure and plant residues on soil organic carbon sequestration in the southern Loess Plateau of China

Increasing soil organic carbon (SOC) sequestration enhances the stability and productivity of agricultural ecosystems. Organic material application is a direct and effective way to maintain and improve SOC sequestration. However, currently, there is little knowledge on efficient practices for combined organic material application to improve SOC sequestration. In this study, we evaluated the effect of three organic materials alone or in combination on SOC sequestration in a 4-year field experiment. Eight treatments were included: control (CK, conventional chemical fertilizer), green manure (G), straw (S), decomposed sheep manure (M), green manure plus straw (GS), green manure plus sheep manure (GM), straw plus sheep manure (SM), green manure, and straw plus sheep manure (GSM). In 2020, decomposed sheep manure application (M, SM, GM and GSM) resulted in the greatest cumulative SOC sequestration (9.5–10.8 Mg C ha−1), followed by those in treatments S (6.1 Mg C ha−1) and GS (6.9 Mg C ha−1). The SOC sequestration efficiency in the M treatment (44.8 %) was greater than that in the others (15.2–34.8 %). A random forest model revealed that organic material quantity and quality, enzyme activity, and microbial community composition were the primary factors determining SOC sequestration. Sheep manure application increased SOC sequestration by increasing lignin quantity and proportion. Incorporating green manure and straw return enhanced SOC sequestration by promoting microbial growth and increasing soil C-acquiring enzyme activity. However, interactions between sheep manure and plant residues resulted in decreases in SOC sequestration efficiency compared with sheep manure application alone. This is because combined fertilization stimulated microbial growth and enzyme activity, causing changes in microbial community structure and accelerating organic material and SOC decomposition. Thus, we do not recommend combining livestock manure with straw or green manure to improve SOC sequestration and soil quality in the southern Loess Plateau.

Limited recovery of soil organic carbon and soil biophysical functions after old field restoration in an agricultural landscape

AbstractThe conversion of woodland ecosystems to agricultural landscapes has led to unprecedented losses of biodiversity and ecosystem functioning globally. Unsustainable agricultural practices have contributed to the degradation of soil's physical and biogeochemical properties. Ecological restoration of unproductive agricultural land is imperative for reversing land degradation and ameliorating the degrading effects of agriculture on biodiversity and ecosystem functions. However, it is unclear to what extent common restoration activities, such as tree planting, can facilitate the recovery of ecosystem condition and in particular, improve soil physical, biogeochemical and biotic components. Here, we investigated how the cessation of cropping, followed by tree planting, affected soil carbon concentrations and key biophysical soil functions. Data were collected across 10 sites a decade after the replanting of woody species on old fields in semi‐arid Western Australia. We applied a chronosequence approach and measured soil functions in fallow cropland (restoration starting point), 10‐year‐old planted old fields and intact woodland reference sites (restoration target point). We stratified sampling between open areas and patches under trees in planted old fields and reference woodlands to account for inherent biophysical differences. Soils under planted trees recovered to some extent, having reduced soil compaction and higher soil penetration depth in comparison with the fallow cropland. However, soils under trees in planted old fields did not reach woodland reference conditions for these properties. Moreover, recovery was not evident for other soil physical, biogeochemical and biotic components such as soil organic carbon, soil moisture, leaf litter and woody debris decomposition rates. Limited recovery of soil functions may be at least partly explained by time lags associated with slow growth rates of planted trees in dry ecosystems. Our study shows that the legacy of cropping can persist over long timeframes in semi‐arid regions, with modest signs of woodland recovery beginning to emerge 10 years after tree planting.

Soil organic carbon increase via microbial assimilation or soil protection against the priming effect is mediated by the availability of soil N relative to input C

Labile C inputs into soils will be partially transformed into soil organic carbon (SOC) through microbial assimilation or physicochemical protection as such mineral-organic interactions and soil aggregation. The C inputs may stimulate the decomposition of native SOC, inducing a phenomenon known as the priming effect. Increasing C inputs may increase SOC content, yet the relative role of these mechanisms in controlling the magnitudes of SOC increase among soils remains unclear. Four soils differing in microbiology and N content were incubated with 13C-labeled glucose at the amounts of 0.5 (G0.5), 1.0 (G1.0), and 2.0 (G2.0) g C kg−1 soil for 48 days. The objectives of this study were 1) to quantify the fates of added glucose-C, the priming effect, and the changes in SOC and mineral N contents after the incubation, and 2) to identify the main mechanisms for SOC increase with the increased amount of C input and the effects of initial soil N availability and microbial composition. 13C isotope probing showed that 19 to 26 % and 37 to 96 % of added glucose were utilized for microbial respiration and growth, respectively, after the incubation in all soils, with the glucose-C use efficiency ranging from 30 to 60 %. The remaining accounted for 4 to 37 % in all cases except for UltisolHN at G1.0 and G2.0 (–23 % and −2%), which was confirmed as the fraction protected in soil or re-utilized by microbes via acid extraction. The soil-protected glucose-C was higher, while glucose-C use efficiency was lower with the increased amount of added glucose only in the soils with low N. Glucose addition induced a positive priming effect, a SOC increase, and a mineral N loss irrespective of soil type and addition amount. Glucose addition increased the cumulative fungal biomass in all cases and the cumulative bacterial biomass only at G2.0 in all soils and at G1.0 in the high-N soils. It increased the final fungal necromass only at G0.5 in MollisolLN and UltisolHN and at G2.0 in MollisolHN and the final bacterial necromass in all cases except for the low-N soils and UltisolHN at G2.0. With the increased amount of added glucose, the SOC content increased linearly and the priming effect and fungal biomass increased non-linearly, with larger magnitudes in the soils with lower N. These results indicated that glucose was quickly protected after addition and remained in the soil until soil N became a limiting factor for microbial utilization. The availability of soil N relative to input C mediated microbial growth and its controls over SOC change via the soil protection and priming effects. The carbon sequestration potential with increased input of dissolved substrates as such glucose e. g. through root exudation was likely larger in soils with lower fertility due to reduced substrate-C use efficiency and increased effect of soil protection despite an increased priming effect. Further studies are needed on more substrate types as they affect substrate-C use efficiency and soil protection mechanisms.

Priming of Soil Organic Carbon Decomposition Induced by Exogenous Organic Carbon Input Depends on Vegetation and Soil Depth in Coastal Salt Marshes

The input of fresh organic carbon into soils can stimulate organic carbon mineralization via priming effects (PEs). However, little is known about the characterization of PEs in coastal wetlands. We investigated the PEs of two salt marshes (Suaeda salsa and Phragmites australis) in the Yellow River Delta by adding 13C-labeled glucose to soils collected from the 0–10 cm and 20–30 cm layers of both salt marshes. The addition of glucose produced a significant positive PE in both soil layers for both vegetation types. There were no differences in the PE of the topsoil layer between the two vegetation types (p > 0.05), whereas the PE of S. salsa was 19.5% higher than that of P. australis in the subsoil layer (p < 0.05). In addition, the topsoil layer showed a higher average PE of 29.1% compared to that of the subsoil layer for both vegetation types (p < 0.05). The differences in the PEs between the two vegetation types and the two layers could be associated with a differential soil salinity, substrate availability, and microbial community structure. Our findings highlight the important role of PEs in regulating the soil carbon storage of coastal salt marshes, which should be considered when assessing and modeling the soil carbon cycling of coastal wetlands.

Enhanced home-field advantage in deep soil organic carbon decomposition: Insights from soil transplantation in subtropical forests

Climate change affects microbial community physiological strategies and thus regulates global soil organic carbon (SOC) decomposition. However, SOC decomposition by microorganisms, depending on home-field advantage (HFA, indicating a faster decomposition rate in ‘Home’ than ‘Away’ conditions) or environmental advantage (EA, indicating a faster decomposition rate in warmer-wetter environments than in colder-drier environments) remains unknown. Here, a soil transplantation experiment was conducted between warmer-wetter and colder-drier evergreen broadleaved forests in subtropical China. Specifically, soil samples were collected along a 60 cm soil profile, including 0–15, 15–30, 30–45, and 45–60 cm layers after one year of transplantation. SOC fractions, soil chemical properties, and microbial communities were evaluated to assess where there was an HFA of EA in SOC decomposition, along with an exploration of internal linkages. Significant HFAs were observed, particularly in the deep soils (30–60 cm) (P < 0.05), despite the lack of a significant EA along a soil profile, which was attributed to environmental changes affecting soil fungal communities and constraining SOC decomposition in ‘Away’ conditions. The soils transplanted from warmer-wetter to colder-drier environments changed the proportions of Mortiereltomycota or Basidiomycota fungal taxa in deep soils. Furthermore, the shift from colder-drier to warmer-wetter environments decreased fungal α-diversity and the proportion of fungal necromass carbon, ultimately inhibiting SOC decomposition in ‘Away’ conditions. However, neither HFAs nor EAs were significantly present in the topsoil (0–30 cm), possibly due to the broader adaptability of bacterial communities in these layers. These results suggest that the HFA of SOC decomposition in deep soils may mostly depend on the plasticity of fungal communities. Moreover, these results highlight the key roles of microbial communities in the SOC decomposition of subtropical forests, especially in deep soils that are easily ignored.

Nitrate-induced hydroxyl radical releases deep soil organic carbon by opening the ‘enzyme latch’ under micro-aerobic conditions

Deep soils (defined here as soil layers >1 m beneath the ground) contain a significant amount of soil organic carbon (SOC) with a relatively slow turnover rate. In oxygen (O2) limit conditions, terms here as “micro-aerobic environment”, a high concentration of phenol usually suppresses SOC decomposition by inhibiting hydrolase activities, a mechanism known as the ‘enzyme latch’. Here, we showed that the addition of nitrate (NO3−) into deep soil significantly decreased the soil phenol content. This reduction alleviated the inhibitory effect of phenol on hydrolase activities, resulting in an increased rate of deep soil SOC decomposition. NO3− addition enhanced deep soil SOC decomposition by opening the ‘enzyme latch’ under micro-aerobic conditions. Under micro-aerobic conditions, NO3− addition increased the concentration of hydroxyl radicals (•OH), with the extent of increase negatively correlated with the soil phenol content. Quenching •OH using terephthalic acid removed the suppressing effect of NO3− on phenol content, indicating that NO3− addition opened the ‘enzyme latch’ by promoting •OH generation, which oxidized phenol. Additionally, the addition of NO3− promoted the production of nicotinamide adenine dinucleotide (NADH) and hydrogen peroxide (H2O2) in deep soil. The H2O2 was significantly positively correlated with •OH, suggesting that the enhanced •OH generation under NO3− addition was caused by the Fenton reaction. Overall, our results shed light on a new pathway through which NO3− leaching affected SOC stability in micro-aerobic deep soils. Reducing nitrate leaching is beneficial for the conservation of deep soil SOC.

Evaluation and optimisation of the soil carbon turnover routine in the MONICA model (version 3.3.1)

Abstract. Simulation models are tools commonly used to predict changes in soil carbon stocks. Prior validation is essential, however, for determining the reliability and applicability of model results. In this study, the process-based biogeochemical model MONICA (Model of Nitrogen and Carbon dynamics on Agro-ecosystems) was evaluated with respect to soil organic carbon (SOC), using long-term monitoring data from 46 German agricultural sites. A revision and parameterisation of equations, encompassing crop- and fertiliser-specific C contents and the abiotic factors of soil temperature, soil water and clay content, were undertaken and included in the model. The modified version was also used for a Morris elementary effects screening method, which confirmed the importance of environmental and management factors to the model's performance. The model was then calibrated by means of Bayesian inference, using the Metropolis–Hastings algorithm. The performance of the MONICA model was compared with that of five established carbon turnover models (CCB, CENTURY, C-TOOL, ICBM and RothC). The original MONICA model systematically overestimated SOC decomposition rates and produced on average a ∼17 % greater mean absolute error (MAE) than the other models. The modification and calibration significantly improved its performance, reducing the MAE by ∼30 %. Consequently, MONICA outperformed CENTURY, CCB and C-TOOL, and produced results comparable with ICBM and RothC. Use of the modified model allowed mostly adequate reproduction of site-specific SOC stocks, while the availability of a nitrogen, plant growth and water submodel enhanced its applicability when compared with models that only describe carbon dynamics.

Pedodiversity and Organic Matter Dynamics in the North Apennines (Italy): Relationships among Soil Types, Biodiversity, and Ecological Functionality

Pedodiversity is generally neglected in studies concerning soil organic carbon (SOC). Therefore, this investigation aimed to explore the effect of soil types on the following: (1) soil processes related to organic matter (OM) dynamics along the profile; and (2) the microbial community and functionality within the uppermost horizon. Humic Dystrudepts (HD), Typic Dystrudepts (TD), and Humic Lithic Dystrudepts (HLD) were selected in beech forests of the Apennine ridge in the Emilia-Romagna Region (Italy). Soils were sampled by horizons until parent material, and physico-chemical and functional analyses were performed. The results showed that both HD and HLD soils had a higher SOC accumulation than TD, particularly within the deeper horizons. Such accumulation might be due to the lower turnover rate of soil OM forms, namely fulvic acid-like substances, humic acid-like substances, and non-extractable OM. Noteworthy, the A horizons showed slight differences in SOC among the soil types, suggesting similar SOC decomposition processes. This fact was confirmed by the lack of differences in microbial DNA-based diversity and functionality. This study highlighted the importance of combining pedodiversity and microbial diversity for a wider perspective on SOC dynamics.

Nitrogen availability mediates the effects of roots and mycorrhizal fungi on soil organic carbon decomposition: A meta-analysis

Nitrogen availability mediates the effects of roots and mycorrhizal fungi on soil organic carbon decomposition: A meta-analysis

Experimental warming accelerates positive soil priming in a temperate grassland ecosystem

Unravelling biosphere feedback mechanisms is crucial for predicting the impacts of global warming. Soil priming, an effect of fresh plant-derived carbon (C) on native soil organic carbon (SOC) decomposition, is a key feedback mechanism that could release large amounts of soil C into the atmosphere. However, the impacts of climate warming on soil priming remain elusive. Here, we show that experimental warming accelerates soil priming by 12.7% in a temperate grassland. Warming alters bacterial communities, with 38% of unique active phylotypes detected under warming. The functional genes essential for soil C decomposition are also stimulated, which could be linked to priming effects. We incorporate lab-derived information into an ecosystem model showing that model parameter uncertainty can be reduced by 32–37%. Model simulations from 2010 to 2016 indicate an increase in soil C decomposition under warming, with a 9.1% rise in priming-induced CO2 emissions. If our findings can be generalized to other ecosystems over an extended period of time, soil priming could play an important role in terrestrial C cycle feedbacks and climate change.

Drought may exacerbate dryland soil inorganic carbon loss under warming climate conditions

Low moisture conditions result in substantially more soil inorganic carbon (SIC) than soil organic carbon (SOC) in drylands. However, whether and how changes in moisture affect the temperature response of SIC in drylands are poorly understood. Here, we report that the temperature sensitivity of SIC dissolution increases but that of SOC decomposition decreases with increasing natural aridity from 30 dryland sites along a 4,500 km aridity gradient in northern China. To directly test the effects of moisture changes alone, a soil moisture control experiment also revealed opposite moisture effects on the temperature sensitivities of SIC and SOC. Moreover, we found that the temperature sensitivity of SIC was primarily regulated by pH and base cations, whereas that of SOC was mainly regulated by physicochemical protection along the aridity gradient. Given the overall increases in aridity in a warming world, our findings highlight that drought may exacerbate dryland soil carbon loss from SIC under warming.

Effect of drainage on microbial transformation processes of soil organic carbon in two typical wetlands of China

Wetlands store one third of global soil organic carbon (SOC) and are strongly affected by artificial drainage. The impact of drainage-induced water-table decline on carbon cycling in different wetlands, particularly microbial transformation processes, remains unclear. To address this knowledge gap, we collected soil samples from two typical wetlands of China (a nutrient-poor bog located in Dajiuhu and a nutrient-rich fen in Hongyuan) and conducted an incubation experiment with the addition of 13C-labeled glucose to analyze the effects of short- and long-term drainage on SOC decomposition, extracellular enzyme activity, microbial carbon use efficiency (CUE), and microbial carbon accumulation efficiency (CAE). The results showed that both short- and long-term drainage significantly increased SOC decomposition rates in both wetlands (from 1.47 μg C·g-1·h-1 in submerged soils to 2.47 μg C·g-1·h-1 in drained soils), microbial biomass carbon derived from glucose (from 0.21 mg C·g-1 to 1.00 mg C·g-1) and CAE (from 0.29 to 0.73), but did not alter CUE (ranging from 0.34 to 0.86). Long-term drainage increased α-glucosidase activity in the Dajiuhu wetland and decreased β-glucosidase and phenol oxidase activities in the Hongyuan wetland. In conclusion, drainage enhanced the 'microbial carbon pump' and its efficiency in wetlands mainly via increasing microbial intracellular metabolism (including respiration), but also acce-lerated SOC decomposition.

Chemical composition and thermal stability of topsoil organic carbon: Influence of cropping system and tillage practices

AbstractAgricultural management practices play a significant role in regulating the potential for soil organic carbon (SOC) sequestration. The objective of this study was to determine the effects of cropping systems and tillage practices on the chemistry and thermal stability of topsoil SOC in a long‐term field study in Ontario, Canada. The cropping system is based on rotations including corn, alfalfa, cereals, soybeans and a red clover cover crop. Tillage practices of conventional (moldboard plow, CT) and conservation (no‐till, NT) were applied to each cropping system. A 130‐day laboratory incubation was conducted to measure the potentially mineralizable SOC. The thermal stability and molecular structure of SOC were investigated using thermal analysis‐programmed pyrolysis (PP) and solid‐state 13C cross polarization/total sideband suppression magic angle spinning nuclear magnetic resonance (CP/TOSS MAS NMR) spectroscopy, respectively. The SOC stocks were larger under NT practices and the crop rotations incorporating alfalfa and cover crops. Under NT practices, an abundance of aromatic‐C components was observed, however, soil under CT showed an abundance of aliphatic‐C compounds (p &lt; 0.001), with a higher alkyl/O‐alkyl‐C ratio, indicating a higher degree of SOC decomposition. Soil under rotations that included soybeans demonstrated a significant increase in aliphatic‐C components, whereas those with cover cropping exhibited an enrichment in O‐alkyl‐C groups (p &lt; 0.05), representing the presence of more resistant and easily decomposable SOC constituents, respectively. The results demonstrated that the thermal stability of SOC in CT systems was higher than that of NT practices (p &lt; 0.05), while NT practices and crop rotations including cover crops are better capable of conserving the labile pool of SOC. Our findings confirmed the correlations among the parameters that characterize both the labile and stable pools of SOC as determined by the methods employed in this study. These results demonstrated that agricultural management practices significantly influence the chemical composition and thermal stability of soil organic matter (SOM), which can have significant impacts on soil health and C sequestration potential.

Effects of Global Warming on Soil Ecosystem Carbon Cycle

The effects of warming due to increased greenhouse gases on the soil carbon cycle have attracted considerable attention. This article presents a comprehensive examination of the fundamental mechanisms implicated in the carbon cycling process inside soil. This article examines various aspects of the soil carbon cycle, including soil respiration, soil apoplastic matter, soil microorganisms, and soil carbon stores. The following findings were derived: The soil microbial community exhibited notable structural alterations in response to rising temperatures. An increase in temperature significantly increases fungal activity in soil microbes. The rise in temperature resulted in an enhanced influx of carbon from vegetation into the soil, thereby facilitating an augmentation in carbon reservoirs within the soil. Increased temperatures have been found to have a positive effect on the process of soil mineralization, leading to the decomposition of soil organic carbon and a subsequent reduction in the storage of carbon within the soil. Elevated temperatures have the additional effect of expediting the process of soil mineralization, which in turn results in the breakdown of soil organic carbon and a subsequent decline in the storage of carbon within the soil. Warming results in long-term declines in soil moisture, and ecosystems in very dry regions may experience reduced carbon uptake. Adaptation of soil respiration to higher temperatures is a more general phenomenon.