Soil Organic Carbon Accumulation Research Articles

Calcium carbonate regulates soil organic carbon accumulation by mediating microbial communities in northern China

Mineral organic complexes are essential for the storage of soil organic carbon (SOC) in agricultural soils. They are also affecting the CO2 emission reduction goals of known as the “doublecarbon target” (carbon peaking and carbon neutrality), as well as a landing point for achieving the 4 per 1,000 carbon enhancement initiative. As a typical soil mineral, calcium (Ca) plays a very critical role in regulating the accumulation of global organic carbon. Although calcium carbonate (CaCO3) has been shown to mediate the SOC accumulation process, especially in northern China, the relationship between Ca and SOC, and the underlying microbial mechanisms remain unclear. In this study, five soils (black soil, light chernozem soil, fluvo-aquic soil, sierozem soil, and loess soil) with different CaCO3 contents (4.29, 17.45, 98.66, 131.85, 143.82 g/kg, respectively) were selected to reveal the relationship among CaCO3, the SOC fraction and the chemical structure, and the bacterial community. The content of CaCO3 was determined by the gas volume method. Solid-state 13C nuclear magnetic resonance (NMR) spectroscopy was used to analyze the chemical structure of SOC, and 16S rRNA gene amplicon sequencing was used to analyze the bacterial community. The results showed that the contents of particulate organic carbon (POC) and mineral-associated organic carbon (MOC) in macro-aggregates were higher than that in micro-aggregates, and that POC was significantly higher than MOC in soil with high CaCO3. With an increase in the CaCO3 content, there was a decrease in the proportion of aromatic C and alkyl C, but an increase in the proportion of O-alkyl C in SOC, the relative abundance of Proteobacteria and Chloroflexi grew, and that of Acidobacteria decreased. Moreover, the overall diversity of the soil bacteria likewise showed a decreasing trend. High CaCO3 soils showed a positive correlation between Acidobacteria and macro-aggregates, and a negative correlation with clay and silt, when compared to low CaCO3 soils. Also, Chloroflexi and Gemmatimonadota showed the opposite relationship with SOC aggregates. CaCO3 influenced the relationship between SOC (fraction and chemical structure) and the bacterial community, resulting in changes in the SOC content within the aggregates. Our results indicate that CaCO3 plays an essential role in the accumulation of SOC and reveal the mechanisms of carbon sequestration in calcareous soils in northern China.

Bacteria life-history strategies and the linkage of soil C-N-P stoichiometry to microbial resource limitation differed in karst and non-karst plantation forests in southwest China

Soil microbial resource-acquisition strategies play a crucial role in soil nutrient cycling and the accumulation of soil organic carbon (SOC) in vegetation restoration. Despite the growing interest in soil microbial resource limitation, the impact of lithology on microbial resource limitation and its relationship with soil carbon–nitrogen-phosphorus (C-N-P) stoichiometry is not well understood. Therefore, we investigated the soil C-N-P and ecoenzymatic stoichiometry, bacterial life-history strategies, and microbial resource limitation in two common plantation forests (Pinus yunnanensis Franch. (PY) and Eucalyptus maideni F. Muell. (EM)) in karst and non-karst areas in southwest China. These areas are characterized by soils derived from limestone and clastic rock, respectively. The results showed that (1) soil nutrients, SOC concentrations and ecoenzymatic activities were significantly higher in karst plantation forests compared to non-karst, except for dissolved inorganic phosphorus; (2) soil microorganisms in both lithology were largely co-limited by C and P in EM plantation while the PY plantation soil in organic horizon primarily limited by P, which might be due to a much higher ratio of soil C:P and N:P; (3) lithology affects the associations between soil C-N-P stoichiometry and microbial resource limitation; (4) redundancy analysis showed that the ratio of C:N acquiring enzyme was a substantially predictor for microbial resource limitation in both karst and non-karst soils; (5) karst soils had a higher proportion of species affiliated with oligotrophs bacteria. Overall, these findings improve our knowledge of microbial resource limitation over limestone and clastic rock and its relationship with soil C-N-P and ecoenzymatic stoichiometry, as well as the lithology effects on bacteria life-history strategies.

Soil calcium prompts organic carbon accumulation after decadal saline-water irrigation in the Taklamakan desert

Soil organic carbon (SOC), as a crucial measure of soil quality, is typically low in arid regions due to salinization, which is a global issue. How soil organic carbon changes with salinization is not a simple concept, as high salinity simultaneously affects plant inputs and microbial decomposition, which exert opposite effects on SOC accumulation. Meanwhile, salinization could affect SOC by altering soil Ca2+ (a salt component), which stabilizes organic matter via cation bridging, but this process is often overlooked. Here, we aimed to explore i) how soil organic carbon changes with salinization induced by saline-water irrigation and ii) which process drives soil organic carbon content with salinization, plant inputs, microbial decomposition, or soil Ca2+ level. To this end, we assessed SOC content, plant inputs represented by aboveground biomass, microbial decomposition revealed by extracellular enzyme activity, and soil Ca2+ along a salinity gradient (0.60–31.09 g kg−1) in the Taklamakan Desert. We found that, in contrast to our prediction, SOC in the topsoil (0–20 cm) increased with soil salinity, but it did not change with the aboveground biomass of the dominant species (Haloxylon ammodendron) or the activity of three carbon-cycling relevant enzymes (β-glucosidase, cellulosidase, and N-acetyl-beta-glucosaminidase) along the salinity gradient. Instead, SOC changed positively with soil exchangeable Ca2+, which increased linearly with salinity. These results suggest that soil organic carbon accumulation could be driven by increases in soil exchangeable Ca2+ under salinization in salt-adapted ecosystems. Our study provides empirical evidence for the beneficial impact of soil Ca2+ on organic carbon accumulation in the field under salinization, which is apparent and should not be disregarded. In addition, the management of soil carbon sequestration in salt-affected areas should be taken into account by adjusting the soil exchangeable Ca2+ level.

Organic amendment effects on cropland soil organic carbon and its implications: A global synthesis

Increasing soil organic carbon (SOC) content can promote soil health and crop yield. Organic amendment application is a common practice to accelerate soil carbon sequestration in cropland. The effects of different organic amendments (e.g., compost, slurry) on SOC are uncertain. Previous studies have investigated SOC response to environmental factors but not well addressed the effect of organic amendment characteristics (e.g., source, liquid/solid form, pH). Depending on 1,972 comparisons from 424 articles, we undertook a meta-analysis approach to explore organic amendment effects on SOC content and the related influence factors. The results show that organic amendment addition increased SOC by an average of 26.9% (or 5.1 Mg C ha−1). Specifically, organic amendments can enhance SOC over the long term (>20 years) or within 1.0 m depth. Organic-residue inputs increased more SOC in regions with an arid climate, alkaline soils, or no-mineral nitrogen application soils than the humid climate regions, acidic soils, and nitrogen application soils, respectively. Sewage sludge and municipal solid waste as organic amendments led to high SOC. The organic amendments' pH and liquid/solid form caused significant differences in SOC accumulation. Amendments with a relatively low carbon content or rich nitrogen content have great potential to increase SOC storage. Our results illustrate the importance of amendment characteristics when estimating the potential of organic amendment addition to soil carbon accumulation. This study highlights that amendment application might be a sustainable strategy to increase soil carbon storage while promoting organic waste utilization.

Predicting changes in soil organic carbon after a low dosage and one-time addition of biochar blended with manure and nitrogen fertilizer

Modeling plays an important role in predicting the long-term effects of biochar on soil organic carbon dynamics. The objective of our study was to apply the Century model to assess changes in temporal soil organic carbon in soil amended with manure and nitrogen fertilizer (MN), with manure and biochar (MB) or with manure, nitrogen fertilizer and biochar (MNB). We determined that, after 115 years, soil organic carbon stocks could not reach a steady state (equilibrium) or pre-cultivation levels, regardless of amendment type. Our results showed that a biennial input of manure and nitrogen fertilizer (MN) led to a 84% increase in soil organic carbon compared to a 79% (MNB) and 70% (MB) increase when amendments contained biochar. However, the quantity of organic matter input from crop residues and amendments was sufficient to increase the active fraction, with a turnover time of months to years, by 86%. In fact, carbon associated with the slow fraction, with a turnover time of 20 to 50 years, was the key driver for soil organic carbon accumulation in all amendment types. Although the passive fraction is the most stable form of carbon in the soil, with a turnover time of 400 to 100 years, once manure and biochar were added to the soil, this fraction increased up to 32%. Our results provided further insight into the ability of Century to accurately predict changes in soil organic carbon stocks when a combination of manure, nitrogen fertilizer or biochar were added to soil. Century predicted soil organic carbon stocks within -1% to +9% of measured values. However, further fine-tuning of the model is required since biochar undergoes chemical transformations (e.g., ageing) and changes soil physical parameters (e.g., bulk density) that can not be currently accounted for in the Century model. Addressing these limitations of Century will also help to increase the relationship between measured and predicted values.

How do harvesting methods applied in continuous-cover forestry and rotation forest management impact soil carbon storage and degradability in boreal Scots pine forests?

Forest management affects soil carbon (C) storage through forest composition, microclimate and litter inputs. How two major forest management systems, continuous-cover forestry (CCF) and clear-cut-based rotation forest management (RFM), differ in their impact on soil C in boreal forests is still poorly understood, however. We compared their effects on soil organic carbon (SOC) storage and quality in boreal Scots pine (Pinus sylvestris L.) dominated forests in eastern Finland. We tested the hypotheses that (1) colder microclimates and continuous litter inputs will lead to higher SOC stocks in CCF plots than in clear-cuts and (2) the more labile litter in clear-cuts with varying ground vegetation will enhance SOC decomposition rates. We sampled uncut mature forests, clear-cuts, retention-cuts and gap-cuts, in which we analysed SOC concentrations and calculated the stocks. We measured stand characteristics such as diameter-at-breast height, basal area, dominant tree height, and understorey species coverage of the various treatments and modelled the above- and belowground litter inputs based on these parameters. We used laboratory incubation and sequential fractionation of SOC to assess its degradability under standardized conditions. To estimate the decomposition rate in the various environments we incubated cellulose bags in situ. We assessed the impact of microclimate on SOC decomposition, using data from soil-temperature and soil-moisture field measurements. We quantified the microbial biomass C pool, using chloroform fumigation extraction to gain insight on the impact of forest management practice on soil microbes. The SOC concentrations and SOC stocks did not differ significantly between the treatments, despite the presence of a warmer microclimate and lower litter inputs in the clear-cut plots. However, we found differences in the quality of the SOC. Soils in clear-cut sites showed lower proportions of labile SOC compounds than did the other treatments. As hypothesized, the decomposition rates were elevated in clear-cuts, but were equally as high within the canopy gaps on gap-cut stands. Our work highlights that forest management affects the quality, degradability, long-term accumulation and storage of SOC. We conclude that the accumulation of labile compounds in uncut forests and retention-cuts, combined with the decreased decomposition rates, indicate a higher potential for future C accumulation in the soil than in clear-cuts.

Ectomycorrhizal effects on decomposition are highly dependent on fungal traits, climate, and litter properties: A model-based assessment

It has been proposed that competition between ectomycorrhizal (ECM) fungi and free-living saprotrophs for resources like nitrogen (N) slows decomposition and increases the soil carbon storage in ECM ecosystems compared to arbuscular (AM) ecosystems. However, empirical evidence for the generality of such ECM effects is equivocal, and confounding mechanisms have been proposed that affect the magnitude and direction of ECM effects on soil carbon. Here we conduct a theoretical modeling experiment, where we explicitly incorporate mycorrhizal processes into the Carbon, Organisms, Rhizosphere, and Protection in the Soil Environment (CORPSE) model. We use the model to explore the conditions under which ECM N acquisition processes can induce stronger saprotrophic N limitation and result in slower decomposition rates and greater soil organic carbon accumulation compared to AM processes. We found that the ECM fungi more strongly inhibited decomposition when litter inputs were N-depleted and relatively recalcitrant and when ECM fungi possessed a strong capacity to mine N from both recalcitrant soil organic matter and microbial necromass. Climate and seasonality also played a role as the ECM competition effect was strongest at low mean annual temperatures and when litterfall peaked seasonally. Priming effects driven by high root exudation rates in ECM-dominated systems could overwhelm the competition effect and reduce soil carbon under some circumstances. The ECM effect on decomposition in our simulations was highly context dependent. Based on our model results, we expect to see a strong ECM competition effect in temperate deciduous and boreal forests with relatively recalcitrant litter inputs, and with ECM fungi that produce oxidases and necromass-degrading enzymes. However, even a relatively strong ECM competition effect on decomposition only increased soil organic carbon accumulation by ∼10%.

LBNF Practices Combined with Crop Diversification Achieves Soil Organic Carbon Principle ‘4p1000’ under Tropical Conditions

Three separate field experiments were carried out at the Agricultural College and Research Institute, TNAU, Madurai, India during 2019-22 with the aim of assessing the possibility of achieving soil organic carbon principle '4p1000' a recent initiative in restoring soil health, through a novel farming system of Low Budget Naturalway Farming by cultivating millets and pulse crops,. The experiments focused on monocropping of millets, sequential multiple cropping and intercropping of millets, and pulses. The studies continuously assessed soil organic carbon status of the cultivated fields to see whether 4p1000 is feasible under tropical conditions. The results of the trials revealed that, despite the LBNF practice of using tree leaf biomass as a source of nutrients, monocropping failed to realize the principle. However, it was feasible to accomplish this when a millet-pulse system was employed and a black gram pulse crop was introduced to the system. The intercropping of pulses and millets would contribute further to the accumulation of soil organic carbon in the cultivated fields. The study proved that the 4p1000 principle is achievable in the tropics.

Analysis of the Effects of Windthrows on the Microbiological Properties of the Forest Soils and Their Natural Regeneration

Windthrows in the forestry fund, which have become more frequent due to the increase in extreme weather events, have had, and continue to have, mostly negative economic and ecological effects, making them a pressing issue in forestry research. The main objectives of this study are to evaluate the effects of windthrows on some microbiological properties of forest soils and to monitor the evolution of the degraded tree regeneration, four years after the event, for three tree species: Norway spruce (Picea abies L.), sessile oak (Quercus petraea), and European beech (Fagus sylvatica L.). The experimental plot used is arranged in dispersed blocks and subdivided plots, with three repetitions, and is bifactorial, with factor A representing the tree species and factor B the windthrows. There are two possibilities: affected by windthrows (AW) and unaffected by windthrows (WW). For each tree species, dehydrogenase activity (DA) and the number of fungi (NF) in the organic horizon at the soil surface were studied. Correlations were highlighted between the differences in AW and WW of Current Dehydrogenase Activity (CDA), Potential Dehydrogenase Activity (PDA), and NF with the number of naturally regenerated seedlings (NRS) and the type of soil. Stimulating NRS in AW forests and increasing the volume of terrestrial organic carbon (TOC) biomass is directly dependent on soil fertility, primarily determined by Soil Organic Carbon (SOC), which accumulates in the soil as a result of organic matter, deposited on the surface. Sustainable forest management of AW plots should stimulate the accumulation of SOC, including the partial or total preservation of dead trees, provided that the attack of specific diseases and pests is avoided.

Effects of Vegetation Types on Carbon Cycle Functional Genes in Reclaimed Soil from Open Pit Mines in the Loess Plateau

Vegetation restoration can effectively improve the ecological environment of mining areas, enhance the ecological service function, and promote the carbon sequestration and sink increase in the ecosystem. The soil carbon cycle plays an important role in the biogeochemical cycle. The abundance of functional genes can predict the material cycling potential and metabolic characteristics of soil microorganisms. Previous studies on functional microorganisms have mainly focused on large ecosystems such as farmland, forest, and wetland, but relatively little attention has been paid to complex ecosystems with great anthropogenic interference and special functions, such as mines. Clarifying the succession and driving mechanism of functional microorganisms in reclaimed soil under the guidance of vegetation restoration is helpful to fully explore how functional microorganisms change with the change in abiotic and biotic conditions. Therefore, 25 topsoil samples were collected from grassland (GL), brushland (BL), coniferous forests (CF), broadleaf forests (BF), and mixed coniferous and broadleaf forests (MF) in the reclamation area of the Heidaigou open pit waste dump on the Loess Plateau. The absolute abundance of soil carbon cycle functional genes was determined using real-time fluorescence quantitative PCR to explore the effect of vegetation restoration on the abundance of carbon cycle-related functional genes in soil and its internal mechanism. The results showed that:① the effects of different vegetation restoration types on the chemical properties of reclaimed soil and the abundance of functional genes related to the carbon cycle were significantly different (P<0.05). GL and BL showed significantly better accumulation of soil organic carbon, total nitrogen, and nitrate nitrogen (P<0.05) than that in CF. ② The gene abundance of rbcL, acsA, and mct was the highest among all carbon fixation genes. The abundance of functional genes related to carbon cycle in BF soil was higher than that in other types, which was closely related to the high activity of ammonium nitrogen and BG enzymes and the low activity of readily oxidized organic carbon and urease in BF soil. The functional gene abundance of carbon degradation and methane metabolism was positively correlated with ammonium nitrogen and BG enzyme activity and negatively correlated with organic carbon, total nitrogen, readily oxidized organic carbon, nitrate nitrogen, and urease activity (P<0.05). ③ Different vegetation types could directly affect soil BG enzyme activity or affect soil nitrate nitrogen content, thus indirectly affecting BG enzyme activity, in turn manipulating the abundance of functional genes related to the carbon cycle. This study is helpful to understand the effects of different vegetation restoration types on the functional genes related to the carbon cycle in the soil of mining areas on the Loess Plateau and provides a scientific basis for ecological restoration and ecological carbon sequestration and sink enhancement in mining areas.

Plant diversity drives soil carbon sequestration: evidence from 150 years of vegetation restoration in the temperate zone.

Large-scale afforestation is considered a natural way to address climate challenges (e.g., the greenhouse effect). However, there is a paucity of evidence linking plant diversity to soil carbon sequestration pathways during long-term natural restoration of temperate vegetation. In particular, the carbon sequestration mechanisms and functions of woody plants require further study. Therefore, we conducted a comparative study of plant diversity and soil carbon sequestration characteristics during 150 years of natural vegetation restoration in the temperate zone to provide a comprehensive assessment of the effects of long-term natural vegetation restoration processes on soil organic carbon stocks. The results suggested positive effects of woody plant diversity on carbon sequestration. In addition, fine root biomass and deadfall accumulation were significantly positively correlated with soil organic carbon stocks, and carbon was stored in large grain size aggregates (1-5 mm). Meanwhile, the diversity of Fabaceae and Rosaceae was observed to be important for soil organic carbon accumulation, and the carbon sequestration function of shrubs should not be neglected during vegetation restoration. Finally, we identified three plants that showed high potential for carbon sequestration: Lespedeza bicolor, Sophora davidii, and Cotoneaster multiflorus, which should be considered for inclusion in the construction of local artificial vegetation. Among them, L. bicolor is probably the best choice.

Maximizing soil organic carbon stocks under cover cropping: insights from long-term agricultural experiments in North America

Cover crops are widely advocated for increasing soil organic carbon (SOC) levels, thereby benefiting soil health improvement and climate change mitigation. Few regional-scale studies have robustly explored SOC stocks under cover cropping, due to limited long-term experiments. We used the unique experimental data from the North American Project to Evaluate Soil Health Measurements conducted in 2019 to address this issue. This study included 19 agricultural research sites with 36 pairs of cover cropping established between 1896 and 2014. Explanatory variables related to site-specific environmental conditions and management practices were collected to identify and prioritize contributing factors that affect SOC stocks with cover crops, by coupling the Boruta algorithm and structural equation modeling. Overall, cover crops significantly (P < 0.05) improved several indicators of soil health, including greater SOC (concentration: +8%; stock: +7%), total nitrogen (+8%), water-stable aggregates (+15%), and potential carbon mineralization (+34%), on average, compared to no cover crop control. Likewise, on average, cover crops sequestered SOC 3.55 Mg C ha-1 (0–15 cm depth), with a sequestration rate of 0.24 Mg C ha-1 yr-1. In addition, we found climate (Hargreaves climatic moisture deficit) was important in explaining the variation of SOC stocks with cover crops, followed by soil properties (e.g., soil clay content). In terms of management practices, cover crop type had a significant positive (0.36) effect on SOC stocks, with non-legumes showing a greater impact, compared to legumes and mixtures. Crop rotational diversity also had a positive (0.28) effect on SOC accumulation. Our findings suggested that integrating non-legume cover crops into diverse crop rotation is likely to be a promising strategy to maximize SOC stocks with cover crops across North America.

Spatial estimation of soil carbon and nitrogen in a grassland shrubland transition

Shrub encroachment via anthropogenic introduction has been used for ecological restoration in degraded desert grassland. However, there have been debates concerning whether this activity can be effective, as contrasting results were frequently reported. The objectives of this study were to address if various Caragana korshinskii planting conditions (planting year and density) had varying influences on soil organic carbon (SOC), soil total nitrogen (STN), and their spatial heterogeneities along the transition from desert grassland to shrubland. We investigated SOC and STN at the community and landscape scales, with the former containing eight land types of enclosed grassland, grazed grassland, and shrubland with varying levels of planting years (3, 12, or 22 years) and planting intervals (2, 6, or 40 m), and the latter consisting of 43 grassland-shrubland mosaic sites (desert grassland, grassland-shrubland edge, and shrubland) covering approximately 2,976 km2 area. At the community scale, the SOC and STN contents from 0 to 100 cm soil depth in shrubland, regardless of varying planting years and densities, were higher than those observed in grazed grassland. Though it appeared that short-term of shrub establishment (3 and 12 years) in shrubland outscored enclosed grassland in SOC accumulation, it was still questionable if this can be consistent for a longer time period as no significant difference was seen for SOC contents between enclosed grassland and shrubland after 22 years of shrub establishment. At the landscape scale, the SOC contents were higher in shrubland than those in desert grassland. However, no significant difference was observed for STN among shrubland and desert grassland. Regarding their spatial heterogeneities, SOC exhibited stronger spatial autocorrelation in grassland-shrubland edge than in desert grassland and shrubland, while STN did not evidently differ in spatial autocorrelation among these transition states. In brief, we have observed differences in soil carbon and nitrogen at community scales, but when crossing over to broad scales do not show the kind of significant spatial heterogeneity that we thought would be present in shrub introductions over the past 30 years. There may be a certain lag in the evolution of soil carbon and nitrogen responses from the introduction of shrubs from the community scale to the landscape scale.

Divergent accumulation of microbial and plant necromass along paddy soil development in a millennium scale

Plant inputs and their subsequent microbial transformations drive the formation and accumulation of soil organic carbon (SOC). Rice paddy is more conducive to SOC accumulation than uplands, primarily because of predominant anaerobic conditions. However, the role of microbes and plants in the buildup of SOC under prolonged rice cultivation has not been well explored in the literature. In a millennium-scale paddy soil chronosequence, we used amino sugars (AS) and lignin phenols (LN) as tracers to investigate microbial and plant-derived necromass changes and evaluated their contributions to SOC accumulation with increasing rice cultivation duration. Across the 1000-year rice cultivation process, AS and LN contents increased with SOC accumulation. Soil pH and salinity are considered to play vital roles in regulating the retention of AS and LN. In contrast to the control of soil enzyme activity on LN accrual (e.g., peroxidase), the microbial biomass and fungi-to-bacteria ratio greatly affected AS accumulation in paddy soil. The components of AS and LN also changed with time, exhibiting a significant accumulation of galactosamine and cinnamyl phenol units in the late stage. Long-term rice cultivation is more conducive to the accumulation of bacterial residues. AS demonstrated a greater contribution to SOC than LN compounds within 100 years, whereas the contribution of LN ultimately exceeded AS in the late stage. Concurrently, we found a higher degree of oxidative lignin degradation in younger soils and reduced degradation with increasing duration of rice paddy cultivation. The accumulation of microbial necromass is more than plant necromass in the early stage, and it is the opposite in the late stage. Our results are critical to understand the formation and sequestration processes of SOC in paddy soils.

Dynamics of litter decomposition rate and soil organic carbon sequestration following vegetation succession on the Loess Plateau, China

Litter quality determines the decomposability of litter and the proportion of recalcitrant residues, which in turn can affect the accumulation of soil organic carbon (SOC). However, the impact of litter decomposition on SOC turnover following vegetation succession has not been systematically studied. To clarify the dynamics and mechanisms of litter decomposition and SOC sequestration following vegetation succession, this study conducted a decomposition experiment across four successional stages: grassland (∼30 years), shrubland (∼60 years), pioneer forest (∼110 years), and climax forest (∼160 years). This study also analyzed the litter quality and the SOC turnover rate. The results showed that litter decomposition rates gradually decreased with vegetation succession. Litter lignin content (LC), and nitrogen content (LN) were the major factors controlling the change of litter decomposition rate. Litter with a high LC: LN ratio and lignin: LN ratio exhibited a lower decomposition rate, whereas the opposite was found for litter with a higher LN content. The increase in the SOC content mainly occurred in the early successional stage (<110 years), with a higher litter decomposition rate and SOC turnover rate. At the later stage (≥110 years), the SOC was close to saturation, together with low rates of litter decomposition and SOC turnover. The variation trend of the mineral-associated organic carbon (MAOC) content was the same as that of the SOC content, resulting from continuous litter inputs. Based on the above results, litter inputs can significantly increase the SOC content in the early successional stage, and soil carbon sequestrations gradually reach saturation in the late successional stage. The findings of this study strengthen our understanding of the changes in litter decomposition and its contribution to SOC sequestration following vegetation succession.

Impact of Induced Natural Organic Carbons on Soil Organic Carbon (SOC), Permeability and Production of Sandy and Clay Soils in Mediterranean Semi-Arid Eco-System

ABSTRACT The effect of amending “barren” sandy and clay soils with different organic origins on soil organic carbon (SOC) accumulation and permeability is not well known. Therefore, proposing desirable practices to improve their qualities and fertility is a major challenge. To improve soil organic carbon, permeability (PR) and productivity, the two barren soil textures were amended with 0.39 and 0.78 tha−1 (ton per hectare) of manure and lignite, respectively, and irrigated with treated wastewater. During the four years of experimentation, the ranges of increase in SOC of sandy and clay soils were 1.9–3.87 kgm−2, and 0.29–1.40 kgm−2, respectively, and in PR of 35.2–69.3% in sandy soils and 39.3–74.8% in clay soils. These improvements have a major effect on nutrient cycling, significantly improving water and nutrient availability to roots and plants. The levels of improvement increase with the amounts of organic compounds introduced, especially in the clay soil amended with 0.78 tha−1. The proportions of mineralized (lost) SOC were 35.3–62.3% in the sandy soils and 1.0–3.1% in the clay soils. The maximum crop weights produced were approximately 41.2 gm−2 in sandy soils and 1152 gm−2 in clay soils. Thus, amendment of barren sandy and clay soils by all three sources of organic carbon was beneficial, especially for the clay soil. achieved the desired objectives. The gain in clay soils is significantly greater than in sandy soils, which require further study. The type of practice desired by farmers will depend on cost and crop yield. Laboratoire Géoressources. Univerversité de Carthage-Centre des Recherches et Technologies des Eaux, B.P. 273, Soliman 8020 (Tunisia).

Responses of soil organic carbon cycle to land degradation by isotopically tracing in a typical karst area, southwest China.

The loss of soil organic carbon (SOC) under land degradation threatens crop production and reduces soil fertility and stability, which is more reflected in eco-sensitive environments. However, fewer studies simultaneously compared SOC variations and δ13CSOC compositions under diverse land uses, especially in karst areas. Soil profiles from two agricultural lands and a secondary forest land were selected to analyze SOC contents and their stable isotope composition (δ13CSOC) in a typical karst area located in southwest China to understand the response of the SOC cycle to land degradation. Moreover, the relationships between SOC contents and mean weight diameter (MWD) and soil erodibility (K) factor were comprehensively analyzed for assessing the response of SOC to soil degradation risk. The mean SOC content was found to be the lowest in abandoned cropland (6.91 g/kg), followed by secondary forest land (9.31 g/kg) and grazing shrubland (34.80 g/kg), respectively. Meanwhile, the δ13CSOC values exhibited the following trend: secondary forest land (mean: -23.79‰) ≈abandoned cropland (mean: -23.76‰) >shrubland (mean: -25.33‰). The isotopic tracing results suggested that plant litter was the main contributor to SOC in the secondary forest land. Whereas abundant nitrogen from goat feces enhanced plant productivity and resulted in additional accumulation of SOC in the grazing shrubland. Conversely, long-term cultivation led to the depletion of SOC sequestration by the loss of calcium. In surface soils, the fractionation of δ13CSOC were considerably affected by the decomposition of SOC by soil microorganisms and covered vegetation rather than agricultural influences. The findings indicate that the cycling of SOC and soil stability in the calcareous soil of southwest China are largely regulated by different land uses and the presence of vegetation cover. The depletion of SOC and soil physical degradation pose significant challenges for abandoned cropland, particularly in the karst area, where land degradation is inevitable. Nevertheless, moderate grazing enhances SOC levels, which is beneficial to the land fertility maintenance in the karst region. Therefore, more emphasis should be placed on the cultivation methods and management strategies for abandoned cropland in the karst area.

Effect of Conservation Tillage on Changes in Soil Aggregate-associated Organic Carbon and Biological Pools to Nitrogen and Straw Alters in RWCS in North-Western India: A Review

To manage this issue, understanding the mineralization process of crop leftovers is helpful. C and N mineralization kinetics in surface-applied and soil-integrated rice and wheat residues were investigated. Rice and wheat residues bind nitrogen in the soil. The use of the residue increased soil organic carbon by 18% and aggregate stability by 55% compared to the control. This study concludes that instead of simply leaving agricultural wastes on the surface, it is best to work them into the soil, where they will decompose more quickly, the mineral N will be released more quickly, more organic matter will be produced, and the soil structure will be improved. Compost amendment was more effective in decreasing macro-aggregate and silt+clay fraction-specific activities than fertilizer NPK. Tillage and residue levels had a significant impact on soil organic carbon accumulation between 0 and 15 centimeters, but not between 15 and 30 centimeters. The SOC content of plots that used raised beds permanently and retained residue was 19.44 g kg-1, but the SOC content of plots that used zero-tilling was only 18.53 g kg-1. SOC levels in puddled rice grafts and conventionally tilled wheat were both 15.86 g kg-1. When compared to plots where the residue was removed, those where it was left but not tilled sequestered 0.91 g kg-1yr-1 SOC. After receiving NT treatments, the concentration of DOC in three different soil depths (bulk, &gt;0.25 mm aggregate, and 0-5 cm soil) increased by 15.5%, 29.5%, and 14.1%, respectively. Increases in MBC ranged from 11.2% to 11.5% to 20%. The 0-50 cm depth SOC stock increased from 49.89 Mg ha-1 to 53.03 Mg ha-1 when the residue was removed. SOC stock was grown by 50 centimeters by rotational farming, but by just 5.35 percent through no-till farming. Bulk soil SOC was 12.9% higher in S treatments compared to NS treatments that removed crop residue, as were &gt;0.25 mm aggregate (11.3%) and 0.25 mm aggregate (14.1%). While NT treatments increased DOC by 15.5%, 29.5%, and 14.1% in bulk soil, &gt;0.25 mm aggregate, and 0.25 mm aggregate in the 0-5 cm soil layer, respectively, CT treatments increased MBC by 11.2%, 11.2%, and 20%. The 0-5 cm soil layer, bulk soil, and &gt;0.25 mm aggregate all saw increases in DOC content of 23.2%, 25.0%, and 37.5% after receiving S treatments compared to NS treatments, while MBC increased by 29.8%, 30.2%, and 24.1%.

Eastern red cedar effects on carbon sequestration and soil quality in the Great Plains

AbstractEastern red cedar (ERC, Juniperus virginiana L.) is a common tree species in agroforestry plantings and has great potential for bioenergy production due to physical and chemical characteristics of its biomass. The objective of this study was to assess the effects of ERC plantings on carbon (C) sequestration and selected soil quality parameters in existing plantings across the northern U.S. Great Plains. Nine locations were selected in five states with mean annual precipitation (MAP) from 446 to 999 mm and mean annual temperature (MAT) from 4.4 to 10.0°C. Infiltration was measured using the twin ring technique at nine sites in each tree planting and adjacent field (crop, pasture, or hay) at each location. Following infiltration measurements, a 4.8 cm‐diameter soil core to 30 cm depth was collected from inside one infiltration ring of each pair for bulk density, pH, aggregate stability, soil organic carbon (SOC), and total nitrogen (TN) analyses. Penetration resistance in 2.5 cm increments to 30 cm depth was measured in the other infiltration ring. SOC stocks under ERC were significantly higher than in the adjacent field soil at five of the locations and, for all locations, averaged 16.8% greater than in the adjacent field. The estimated SOC accumulation rate for the eight locations with uniform tree stand age averaged 0.30 Mg C ha−1 year−1. Most locations had higher TN and C/N and lower bulk density beneath ERC. Fewer differences for infiltration and penetration resistance and smaller and less consistent differences for pH and aggregate stability were observed. Tree aboveground C stocks were estimated to increase an average of 2.05 Mg C ha−1 year−1. Estimated tree aboveground biomass C and SOC stocks under ERC and in adjacent fields were strongly correlated with MAP. Potential ERC planting for C sequestration or bioenergy feedstock production is not likely to significantly degrade soil quality and may improve soil physical or chemical quality for locations in the US Great Plains.

Trait-based assembly of arbuscular mycorrhizal fungal communities determines soil carbon formation and retention.

Fungi are crucial for soil organic carbon (SOC) formation, especially for the more persistent mineral-associated organic C (MAOC) pool. Yet, evidence for this often overlooks arbuscular mycorrhizal fungi (AMF) communities and how their composition and traits impact SOC accumulation. We grew sudangrass with AMF communities representing different traits conserved at the family-level: 1) competitors, from the Gigasporaceae family; 2) ruderals, from the Glomeraceae family; or 3) both families combined. We labeled sudangrass with 13 C-CO2 to assess AMF contributions to SOC, impacts on SOC priming, and fungal biomass persistence in MAOC. Single-family AMF communities decreased total SOC by 13.8%, likely due to fungal priming. Despite net SOC losses, all AMF communities contributed fungal C to soil but only the Glomeraceae community initially contributed to MAOC. After a month of decomposition, both the Glomeraceae and mixed-family communities contributed to MAOC formation. Plant phosphorus uptake, but not hyphal chemistry, was positively related to AMF soil C and MAOC accumulation. AMF contribution to MAOC is dependent on the specific traits of the AMF community and related to phosphorus uptake. These findings provide insight into how variations in AMF community composition and traits, and thus processes like environmental filtering of AMF, may impact SOC accumulation.