Dynamics Of Soil Organic Carbon Pools Research Articles

Effect of polyethylene microplastics on soil organic carbon pool dynamics in the soil-rhizosphere-alfalfa system

The effect of microplastics (MPs) on soil organic carbon (SOC) has become a growing concern. However, most studies have focused on the effect in a single soil system, and little is known about how MPs affect the soil carbon pool in the soil-plant system. In this study, a 90-day pot experiment was conducted with different concentrations (0%, 0.5%, 1%, and 5% w/w) and exposure times (30d, 60d, and 90d) of polyethylene microplastics to investigate their effects on SOC pools. The results showed that MPs increased particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) pools, while decreasing microbial biomass carbon (MBC). Initially, MPs increased POC by disguise and their effects on enzyme activities and C degradation genes, and indirectly increased MAOC by affecting dissolved organic carbon (DOC) levels (via soil pH) and stimulating enzyme activities. However, as alfalfa rapidly grew from the branching to the flowering stage, plants inputted C into the POC pool via rhizodeposition, while activating and absorbing the MAOC pool for growth through roots, resulting in an increase in POC and a decrease in MAOC. Moreover, plants had priming effects on soil MBC, enzyme activities, and C degradation genes, further influencing SOC pools. Overall, MPs affected plant growth and soil carbon pools by altering soil properties, while plants in turn influenced soil organic carbon pools and the impact of MPs on soil properties. This study provides deeper insights into the effect of MPs on SOC dynamics in the soil-rhizosphere-plant system.

Frozen carbon is gradually thawing: Assessing interannual dynamics of thawed soil organic carbon stocks in the Tibetan Plateau permafrost area from 1901−2020

Large amounts of frozen carbon stored in the permafrost of the Tibetan Plateau (TP) are gradually thawing due to climate warming. The thaw of frozen carbon allows more active soil organic carbon (SOC) on the TP to participate in the global carbon cycle, which has usually been neglected in previous studies of permafrost carbon. This paper assesses the thawed SOC stock and its historical dynamics in TP permafrost areas based on a data-driven scheme. The results show that the current permafrost area of the TP is 1.14 × 106 km2, and the SOC stock in the top 10 m of permafrost areas is 47.36 Pg. The active layer of the TP permafrost has a regional average thickness of 2.37 m during the baseline period (2000−2020), storing 18.19 Pg of SOC, accounting for about 38.4 % of the total SOC stock in the top 10 m, with the remaining more than 60 % perennially frozen in permafrost. The dynamics of thawed SOC are calculated based on baseline period SOC pools. Despite significant fluctuations, there is a general trend of 0.074 Pg SOC thaw per decade over 1901−2020 as the active layer has deepened. Significantly, the thaw trend of frozen SOC after 1976 is more prominent, reaching 0.420 Pg decade−1. Moreover, this paper reconstructs the SOC pool at the beginning of the last century by incorporating historical deep carbon emissions (1 − 10 m) in the current SOC pool. It recalculates the thaw trend of frozen carbon based on this and finds that the general thaw trend of SOC from 1901−2020 is more significant, with a rate of 0.092 Pg decade−1. Additionally, the dynamics of SOC pools in surface soils (0 − 1 m) of TP permafrost areas are also discussed. Our study highlights the importance of permafrost carbon thaw and provides valuable information for TP carbon studies.

Effects of nitrogen-enriched biochar on subtropical paddy soil organic carbon pool dynamics

Agronomic management practices present an opportunity to improve the sustainability of crop production, including reductions of greenhouse gas emissions through impacts on soil organic carbon (SOC) dynamics. We investigated the impacts of contrasting application rates of nitrogen (N)-enriched biochar (4 and 8 t ha−1) on the concentrations of total and active SOC, microbial biomass carbon (MBC), soil aggregates, and the carbon (C) pool management index (CPMI) as an indicator of soil quality in tillering and mature subtropical early and late rice in China. Soil salinity and soil bulk density increased, and soil water content generally decreased under the application of N-enriched biochar at 4 t ha−1. Following the application of the biochar, there were greater soil concentrations of SOC and lower concentrations of dissolved organic-C and active labile organic‑carbon, indicating reduced mineralization and enhanced stocks of stable-C. Biochar application (4 and 8 t ha−1) led to lower soil Ca-SOC concentrations and greater soil Fe(Al)-SOC concentrations. Concentrations of Fe(Al)-SOC were greater under the application of N-enriched biochar at 4 t ha−1, indicating the bonding capacity of iron‑aluminum oxide and organic carbon provided by biochar improved levels of SOC fixation. The composition of soil aggregates under each treatment was mainly micro-aggregates (<0.25 mm). The greater soil content of macro-aggregates (>0.25 mm) increased under amendment with 4 t of biochar ha −1 and the greater SOC content led to greater soil aggregate stability. Levels of C pool activity, C pool index, and CPMI reduced following application of the biochar, while C pool activity index increased slightly, indicating an increase in soil quality. These results indicate that the application of N-enriched biochar during rice cultivation may lead to reductions in SOC mineralization and C emissions and increases in soil C sink capacity, due to greater SOC pool stability, thus improving the sustainability of paddy rice production.

Vertical distribution of different pools of soil organic carbon under long-term fertilizer experiment on rice-wheat sequence in mollisols of North India

ABSTRACT A profound consideration of soil organic carbon (SOC) and SOC pools as affected by the long-term use of fertilizer in a fixed crop sequence is essential to understand and maintain the health and productivity of soil. The dynamics of SOC pools, i.e. total soil organic carbon (TOC) and its different fractions under a rice-wheat cropping system subjected to various fertilizer management strategies over 42 years was investigated near Uttarakhand, India. The soil at the experimental site was an Aquic Hapludoll consisting of a poorly drained silty clay loam (1–1.5 m deep) overlying loamy to sandy sediments. Over 42 years, application of 100% NPK+ FYM (Farm Yard Manure) was the most effective management system in increasing organic C up to 0 to 60 cm soil depths under rice-wheat sequence. The combination of this integrated input application (100% NPK + 15 t ha−1 FYM) significantly built organic carbon fractions like total organic carbon, microbial biomass C (MBC), particulate organic C (POC), KMnO4 oxidizable C, Humic C, Fulvic C, Humin C, water-soluble carbon and hot water extractable carbohydrates at all four soil depths. Hence, application of FYM along with NPK resulted in a significant positive building up of all pools in the treatment at all four depths. Therefore, balance fertilization is panaceally important for sustaining improved soil health with balanced organic status and production potentiality of the soil for rice-wheat cropping sequence.

Effects of ant disturbance on soil organic carbon cycle: A review.

The impact of ants, as consumer and decomposer in ecosystems, on soil organic carbon pool is a hotspot in soil fauna research. Recently, effects of ants on soil organic carbon pool dynamics have been mainly documented in terms of soil macro-elements storage, physical and chemical properties, and microbial community. We summarized the effects of ant disturbance on soil organic carbon cycle. Ant nesting alters microhabitat, microclimate, and physicochemical properties of ant nested soils. By re-shaping soil microbial community structure, regulating the succession process and pattern of vegetation, ant nesting directly or indirectly affects the source, allocation, stability, and microcosmic molecular characteristics of soil organic carbon, scaling from micro, local, to landscape scale. In the future, more attentions should be paid on quantifying the contribution of ant disturbance combined with the fluctuations in environmental factors to soil carbon flux dynamics, establishing quantitative model to link and unify ant-induced soil carbon cycle process, and clari-fying mechanisms underlying the impacts of ants on the stability of soil organic carbon pool, and finally revealing the "ecological engineers" role of ants in regulating soil organic carbon cycling.

Soil carbon pools under long-term rice-wheat cropping system in Inceptisols of Indian Himalayas

ABSTRACTKnowledge about soil organic carbon (SOC) stock and its allocation into different pools is important for global food and environmental security. Accordingly, an attempt is made in the present study to investigate into the dynamics of SOC pools i.e. total soil organic carbon (TOC), oxidisable organic carbon (OC) and its different fractions viz. very labile (CVL), labile (CL), less labile (CLL) and non-labile (CNL) in soils under a 26 years old long-term experiment with rice (Oryza sativa L) – wheat (Triticum aestivum L) cropping system on Inceptisols under humid agro-climatic region of India with different soil management practices (control, 100% recommended dose of NPK, and 50% recommended dose of NPK + 50% N through farmyard manure (FYM). Of the several pools analyzed, a higher proportion of C was found in labile pool followed by very labile, non-labile, and less labile ones constituting about 46, 26.5, 20 and 7.3% of the total organic C at surface soil. The NPK+FYM treatment was found to have higher SOC pools, lability index (LI), recalcitrance indices and stratification ratio as compared to others. Results indicated that balanced fertilization with inorganic and organics is important for maintaining overall sustainability of the rice-wheat system.