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The use of fertilizers is mainly adopted in arid regions to improve the soil carbon (C) pool and crop productivity. However, the mechanisms underlying improvements in dryland wheat field soils related to microbial metabolic activity and community structure remain poorly understood. Therefore, a field experiment with four fertilization treatments and no fertilizer as the control (CK) was conducted for 10 years in a semi-arid region of China. The results revealed that the combined application of chemical and organic fertilizers (fermented chicken manure) clearly increased the levels of soil organic carbon (SOC), dissolved organic carbon (DOC), and light-fraction organic carbon (LFOC) by 13.54–16.72%, 6.96–9.01%, and 11.00–13.51%, respectively, compared to the sole use of chemical fertilizers (FP treatment). Moreover, the combined treatment not only enhanced the metabolic activity of microorganisms concerning carbon source utilization but also increased the diversity of the bacterial community. This caused noticeable changes in the composition of the bacterial community. A Mantel test analysis revealed that Bacteroidetes and Mortierellomycota significantly enhanced the metabolic activity associated with carbohydrate, amino acid, and carboxylic acid C sources. Actinobacteria, Bacteroidetes, and Mortierellomycota facilitated the accumulation of active C and particulate organic carbon (POC), whereas Mortierellomycota specifically promoted the accumulation of heavy-fraction organic carbon (HFOC), thereby collectively influencing the SOC content. The combined application of chemical and organic fertilizers increased the abundance of Bacteroidetes and Mortierellomycota. This enhancement improved the metabolic utilization of carbohydrates, amino acids, and carboxylic acids, resulting in alterations in the types and quantities of soil metabolites. Consequently, these alterations ultimately affect the composition and quantity of the SOC pool in arid agroecosystems. In conclusion, the combined application of balanced NPK fertilizers and organic fertilizers has a strong positive effect in improving soil microbial activity and the soil C pool. [ABSTRACT FROM AUTHOR]

Increased atmospheric nitrogen (N) deposition has greatly influenced soil organic carbon (SOC) dynamics. Currently, the response of SOC to atmospheric N deposition is generally detected through understory N addition, while canopy processes have been largely ignored. In the present study, canopy N addition (CN) and understory N addition (UN, 50 and 100 kg N ha−1 year−1) were performed in a Moso bamboo forest to compare whether CN and UN addition have consistent effects on SOC and SOC turnover times (τsoil: defined as the ratio of SOC stock and soil heterotrophic respiration) with a local NHx:NOy ratio of 2.08:1. The experimental results showed that after five years, the SOC content of canopy water addition without N addition (CN0) was 82.9 g C kg−1, while it was 79.3, 70.7, 79.5 and 74.5 g C kg−1 for CN50, CN100, UN50 and UN100, respectively, and no significant difference was found for the SOC content between CN and UN. Five-year N addition did not significantly change τsoil, which was 34.5 ± 7.4 (mean ± standard error) for CN0, and it was 24.9 ± 4.8, 22.4 ± 4.9, 30.5 ± 4.0 and 22.1 ± 6.5 years for CN0, CN50, CN100, UN50 and UN100, respectively. Partial least squares structural equation modeling explained 93% of the variance in τsoil, and the results showed that soil enzyme activity was the most important positive factor controlling τsoil. These findings contradicted the previous assumption that UN may overestimate the impacts of N deposition on SOC. Our findings were mainly related to the high N deposition background in the study area, the special forest type of Moso bamboo and the short duration of the experiment. Therefore, our study had significant implications for modeling SOC dynamics to N deposition for high N deposition areas. [ABSTRACT FROM AUTHOR]

Coastal reclamation alters the ecological environment of wetlands and influences global carbon cycles. However, variations in soil organic carbon fractions and stability in the soil profile during reclamation, particularly in the subsoil, remain unclear. In this study, soil aggregate‐associated organic carbon and its stability were investigated in soil profiles (0–100 cm) at different reclamation times (0, 24, 44, and 64 years) in coastal poplar plantations in East China. Total soil organic carbon concentrations in the topsoil (0–40 cm) increased with increasing reclamation time but varied little in the subsoil (40–100 cm). In the topsoil, the soil organic carbon concentrations in different aggregate fractions tended to increase with increasing reclamation time, which was enhanced mainly by particulate organic carbon within macro‐aggregates. In the subsoil, soil organic carbon concentrations increased in the micro‐aggregate fraction and decreased in the silt and clay fraction with increasing reclamation time, whereas the opposite changes led to smaller variations in total soil organic carbon. This relative balance was regulated by micro‐aggregate formation via new organic matter input (e.g., root litter) and old mineral‐associated organic carbon depletion. Regardless of the soil horizon, soil aggregate stability increased with reclamation time, whereas the total particulate organic carbon/mineral‐associated organic carbon ratio increased with increasing reclamation time, implying that the soil organic carbon stability decreased, which may be attributed to an increase in the vulnerability of soil organic matter to mineralization as the reclamation progresses. These findings indicate that long‐term plantation development influences aggregate‐associated organic carbon accrual throughout the soil profile in reclaimed coastal land. Thus, effective management is required to improve soil organic carbon accrual in coastal woodland subsoil, which is crucial for increasing soil carbon sequestration. [ABSTRACT FROM AUTHOR]

BACKGROUND: Improvements in farmland soil organic carbon (SOC) stock enhance crop yield and soil fertility while mitigating climate change. Rational fertilization in agricultural production is crucial for safeguarding SOC stock. In this study, field experiments were conducted with different ratios of chemical fertilizer reduction and organic fertilizer substitution for three consecutive years (2018--2020) to explore their effects and interlinkages on SOC fractions, soil properties and SOC stock. RESULTS: The results showed that organic fertilizer substitution increased SOC and its fractions content, SOC stock (by 3.98-- 12.98% and 7.15--18.13%) and soil fertility index (by 11.76--49.26% and 33.33--91.47%) compared to conventional fertilization in 2019 and 2020, while chemical fertilizer reduction had the opposite effect. Moreover, soil properties (except total nitrogen to total phosphorus ratio, N/P) and SOC fractions significantly affected SOC stock, with SOC fractions contributing more than soil properties. The high sensitivity of microbial biomass carbon (MBC) and dissolved organic carbon (DOC) can indicate changes in soil carbon pool. Structural equation modeling (SEM) revealed that organic fertilizer substitution increased SOC content and stock by increasing SOC fractions [recalcitrant organic carbon (ROC) and labile organic carbon (LOC) fractions] content and soil fertility. CONCLUSIONS: Our study revealed the corresponding mechanisms of the two fertilization modes affecting SOC stock changes. The use of organic fertilizer substitution is recommended to increase SOC stocks and soil fertility in wheat fields. [ABSTRACT FROM AUTHOR]

The global warming-driven poleward expansion of mangrove habitats (e.g., Avicennia germinans and Rhizophora mangle) into temperate salt marshes (e.g., Spartina alterniflora and Juncus roemerianus) has been shown to alter coastal soil organic carbon (SOC) storage. However, the taxa-specific consequences of this vegetation shift on the origin and size of SOC sub-fractions (particulate OC (POC); mineral-associated OC (MAOC); and reactive iron-associated OC (FeR-MAOC)) remain largely unexplored. In this study, we used a particle size-based SOC fractionation method to compare quantity and δ13C composition of bulk and each SOC sub-fractions in soil cores collected from Apalachicola Bay barrier islands in Florida, USA, the highest latitude where monospecific communities of all four aforementioned plants co-occur. Depth-dependent variation of bulk soil δ13C clearly showed the global warming-driven replacement of S. alterniflora by mangroves, as well as reciprocal substitutions of S. alterniflora and J. roemerianus, probably driven by changes in wetland elevation. Higher OC burial rates in mangrove habitats suggested that mangrove soils were principally developed by particle deposition. In contrast, comparatively lower OC burial rates but higher OC stocks in salt marsh habitats illustrated subsurface OC input from salt marsh roots. POC was primarily derived from contemporary plant detritus; its concentration was higher in salt marsh habitats (58.8 ± 9.0 % of SOC) relative to mangroves (38.4 ± 6.0 % of SOC). In contrast, MAOC content did not vary across plant habitats (53.5 ± 10.9 % of SOC), and principally originated from microbially-transformed OC and pre-existing plants. FeR-MAOC was essentially absent in R. mangle soils (2.9 ± 3.6 % of SOC) while representing a minor fraction of MAOC in three other plant habitats (7.8 ± 7.0 % of SOC). The δ13C of FeR-MAOC was more like the present-day surface plants, highlighting the in situ FeR-MAOC formation in their active oxidizing rhizospheres.

The form and distribution of organic carbon in soil affect its stability and storage, and nitrogen (N) fertilization can affect the transformation and accumulation of soil organic carbon (SOC), whereas how the N fertilizer rate affects SOC storage by regulating its fractions in a potato continuous cropping system is unknown. A 6-year field experiment was conducted to study the effect of different N fertilizer rates (NE (Nutrient Expert) –N, NE–1/2N, NE, and NE+1/2N) on the changes in SOC and its fractions in a potato continuous cropping system in North China. Soil NO3−-N gradually increased with increasing N fertilizer rates, whereas the N fertilizer rate had less effect on NH4+-N. Compared with the NE−N treatment, the increasing N fertilization increased the SOC and its components, whereas these C fractions did not continue to increase or began to decrease after N fertilization exceeded the rate applied in the NE treatment. While the increase in mineral-associated organic C (MAOC; 16.1–17.2% and 26.1–52.7% in the 0–20 cm and 20–40 cm layers, respectively) was greater than that of particulate organic C (POC; 3.7–7.4% and 11.5–16.4% in the 0–20 cm and 20–40 cm layers, respectively), the increase in bacterial necromass C (BNC; 9.2–21.8% and 28.9–40.4% in the 0–20 cm and 20–40 cm layers, respectively) was greater than that of fungal necromass C (FNC; 6.2–10.1% and 7.1–24.9% in the 0–20 cm and 20–40 cm layers, respectively). Furthermore, the increase in FNC was greater than that of BNC in the 20–40 cm layer of the same treatment. SOC was significantly and positively correlated with MAOC and FNC, and the correlation between SOC and both MNC and FNC was more significant in the 20–40 cm layer than in the 0–20 cm layer. Overall, in the potato continuous cropping system in North China, N fertilization improved SOC storage by increasing MNC to form MAOC, and optimizing N fertilization based on the NE system could better balance the increase and mineralization loss of SOC to achieve high SOC sequestration. [ABSTRACT FROM AUTHOR]

The application of nitrogen fertilizer is crucial in the cultivation of bamboo forests, and comprehending the alterations in soil organic carbon (SOC) due to nitrogen application is essential for monitoring soil quality. Predicting the dynamics of soil carbon stock involves analyzing two components: particulate organic carbon (POC) and mineral-associated organic carbon (MAOC). This study aimed to investigate the impact of high nitrogen inputs on SOC stock in Moso bamboo forests located in southwestern China. The research focused on analyzing changes in soil chemical properties, SOC content, and its components (POC and MAOC), as well as microbial biomass in the surface layer (0–10 cm) under different nitrogen applications (0, 242, 484, and 726 kg N ha−1 yr−1). The results indicate that nitrogen application significantly reduced the SOC content, while concurrently causing a significant increase in POC content and a decrease in MAOC content within the Moso bamboo forest (p < 0.05). The HM treatment notably increased the NO3−-N content to 2.15 mg/kg and decreased the NH4+-N content to 11.29 mg/kg, although it did not significantly influence the microbial biomass carbon (MBC) and nitrogen (MBN). The LN and MN treatments significantly reduced the MBC and MBN contents (71.6% and 70.8%, 62.5% and 56.8%). Nitrogen application significantly increased the Na+ concentration, with a peak observed under the LN treatment (135.94 mg/kg, p < 0.05). The MN treatment significantly increased the concentrations of Fe3+ and Al3+ (p < 0.05), whereas nitrogen application did not significantly affect Ca2+, Mg2+ concentration, and cation exchange capacity (p > 0.05). Correlation and redundancy analyses (RDAs) revealed that the increase in annual litterfall did not significantly correlate with the rise in POC, and changes in extractable cations were not significantly correlated with the decrease in MAOC. Soil nitrogen availability, MBC, and MBN were identified as the primary factors affecting POC and MAOC content. In conclusion, the application of nitrogen has a detrimental impact on the soil organic carbon (SOC) of Moso bamboo forests. Consequently, it is imperative to regulate fertilization levels in order to preserve soil quality when managing these forests. Our research offers a theoretical foundation for comprehending and forecasting alterations in soil carbon stocks within bamboo forest ecosystems, thereby bolstering the sustainable management of Moso bamboo forests. [ABSTRACT FROM AUTHOR]

The use of fertilizers is mainly adopted in arid regions to improve the soil carbon (C) pool and crop productivity. However, the mechanisms underlying improvements in dryland wheat field soils related to microbial metabolic activity and community structure remain poorly understood. Therefore, a field experiment with four fertilization treatments and no fertilizer as the control (CK) was conducted for 10 years in a semi-arid region of China. The results revealed that the combined application of chemical and organic fertilizers (fermented chicken manure) clearly increased the levels of soil organic carbon (SOC), dissolved organic carbon (DOC), and light-fraction organic carbon (LFOC) by 13.54–16.72%, 6.96–9.01%, and 11.00–13.51%, respectively, compared to the sole use of chemical fertilizers (FP treatment). Moreover, the combined treatment not only enhanced the metabolic activity of microorganisms concerning carbon source utilization but also increased the diversity of the bacterial community. This caused noticeable changes in the composition of the bacterial community. A Mantel test analysis revealed that Bacteroidetes and Mortierellomycota significantly enhanced the metabolic activity associated with carbohydrate, amino acid, and carboxylic acid C sources. Actinobacteria, Bacteroidetes, and Mortierellomycota facilitated the accumulation of active C and particulate organic carbon (POC), whereas Mortierellomycota specifically promoted the accumulation of heavy-fraction organic carbon (HFOC), thereby collectively influencing the SOC content. The combined application of chemical and organic fertilizers increased the abundance of Bacteroidetes and Mortierellomycota. This enhancement improved the metabolic utilization of carbohydrates, amino acids, and carboxylic acids, resulting in alterations in the types and quantities of soil metabolites. Consequently, these alterations ultimately affect the composition and quantity of the SOC pool in arid agroecosystems. In conclusion, the combined application of balanced NPK fertilizers and organic fertilizers has a strong positive effect in improving soil microbial activity and the soil C pool.

Increased atmospheric nitrogen (N) deposition has greatly influenced soil organic carbon (SOC) dynamics. Currently, the response of SOC to atmospheric N deposition is generally detected through understory N addition, while canopy processes have been largely ignored. In the present study, canopy N addition (CN) and understory N addition (UN, 50 and 100 kg N ha−1 year−1) were performed in a Moso bamboo forest to compare whether CN and UN addition have consistent effects on SOC and SOC turnover times (τsoil: defined as the ratio of SOC stock and soil heterotrophic respiration) with a local NHx:NOy ratio of 2.08:1. The experimental results showed that after five years, the SOC content of canopy water addition without N addition (CN0) was 82.9 g C kg−1, while it was 79.3, 70.7, 79.5 and 74.5 g C kg−1 for CN50, CN100, UN50 and UN100, respectively, and no significant difference was found for the SOC content between CN and UN. Five-year N addition did not significantly change τsoil, which was 34.5 ± 7.4 (mean ± standard error) for CN0, and it was 24.9 ± 4.8, 22.4 ± 4.9, 30.5 ± 4.0 and 22.1 ± 6.5 years for CN0, CN50, CN100, UN50 and UN100, respectively. Partial least squares structural equation modeling explained 93% of the variance in τsoil, and the results showed that soil enzyme activity was the most important positive factor controlling τsoil. These findings contradicted the previous assumption that UN may overestimate the impacts of N deposition on SOC. Our findings were mainly related to the high N deposition background in the study area, the special forest type of Moso bamboo and the short duration of the experiment. Therefore, our study had significant implications for modeling SOC dynamics to N deposition for high N deposition areas.

Litter decomposition is the main source of soil organic carbon (SOC) pool, regarding as an important part of terrestrial ecosystem C dynamics. The turnover of SOC is mainly regulated by extracellular enzymes secreted by microorganisms. However, the response mechanism of soil C-degrading enzymes and SOC in litter decomposition remains unclear. To clarify how SOC fraction dynamics respond to C-degrading enzymes in litter decomposition, we used field experiments to collect leaf litter and SOC fractions from the underlying layer in Robinia pseudoacacia plantations on the Loess Plateau. Our results showed that SOC, easily oxidizable organic C, dissolved organic C, and microbial biomass C increased significantly during the decomposition process. Litter decomposition significantly decreased soil hydrolase activity, but slightly increased oxidase activity. Correlation analysis results showed that SOC fractions were significantly positively correlated with the litter mass, lignin, soil moisture, and oxidase activity, but significantly negatively correlated with cellulose content and soil pH. Partial least squares path models revealed that soil C-degrading enzymes can directly or indirectly affect the changes of soil C fractions. The most direct factors affecting the SOC fractions of topsoil during litter decomposition were litter lignin and cellulose degradation, soil pH, and C-degrading enzymes. Furthermore, regression analysis showed that the decrease of SOC stability in litter decomposition was closely related to the decrease of soil hydrolase to oxidase ratio. These results highlighted that litter degradation-induced changes in C-degrading enzyme activity significantly affected SOC fractions. Furthermore, the distribution of soil hydrolases and oxidases affected the stability of SOC during litter decomposition. These findings provided a theoretical framework for a more comprehensive understanding of C turnover and stabilization mechanisms between plant and soil. [ABSTRACT FROM AUTHOR]

The form and distribution of organic carbon in soil affect its stability and storage, and nitrogen (N) fertilization can affect the transformation and accumulation of soil organic carbon (SOC), whereas how the N fertilizer rate affects SOC storage by regulating its fractions in a potato continuous cropping system is unknown. A 6-year field experiment was conducted to study the effect of different N fertilizer rates (NE (Nutrient Expert) –N, NE–1/2N, NE, and NE+1/2N) on the changes in SOC and its fractions in a potato continuous cropping system in North China. Soil NO3−-N gradually increased with increasing N fertilizer rates, whereas the N fertilizer rate had less effect on NH4+-N. Compared with the NE−N treatment, the increasing N fertilization increased the SOC and its components, whereas these C fractions did not continue to increase or began to decrease after N fertilization exceeded the rate applied in the NE treatment. While the increase in mineral-associated organic C (MAOC; 16.1–17.2% and 26.1–52.7% in the 0–20 cm and 20–40 cm layers, respectively) was greater than that of particulate organic C (POC; 3.7–7.4% and 11.5–16.4% in the 0–20 cm and 20–40 cm layers, respectively), the increase in bacterial necromass C (BNC; 9.2–21.8% and 28.9–40.4% in the 0–20 cm and 20–40 cm layers, respectively) was greater than that of fungal necromass C (FNC; 6.2–10.1% and 7.1–24.9% in the 0–20 cm and 20–40 cm layers, respectively). Furthermore, the increase in FNC was greater than that of BNC in the 20–40 cm layer of the same treatment. SOC was significantly and positively correlated with MAOC and FNC, and the correlation between SOC and both MNC and FNC was more significant in the 20–40 cm layer than in the 0–20 cm layer. Overall, in the potato continuous cropping system in North China, N fertilization improved SOC storage by increasing MNC to form MAOC, and optimizing N fertilization based on the NE system could better balance the increase and mineralization loss of SOC to achieve high SOC sequestration.

The application of nitrogen fertilizer is crucial in the cultivation of bamboo forests, and comprehending the alterations in soil organic carbon (SOC) due to nitrogen application is essential for monitoring soil quality. Predicting the dynamics of soil carbon stock involves analyzing two components: particulate organic carbon (POC) and mineral-associated organic carbon (MAOC). This study aimed to investigate the impact of high nitrogen inputs on SOC stock in Moso bamboo forests located in southwestern China. The research focused on analyzing changes in soil chemical properties, SOC content, and its components (POC and MAOC), as well as microbial biomass in the surface layer (0–10 cm) under different nitrogen applications (0, 242, 484, and 726 kg N ha−1 yr−1). The results indicate that nitrogen application significantly reduced the SOC content, while concurrently causing a significant increase in POC content and a decrease in MAOC content within the Moso bamboo forest (p < 0.05). The HM treatment notably increased the NO3−-N content to 2.15 mg/kg and decreased the NH4+-N content to 11.29 mg/kg, although it did not significantly influence the microbial biomass carbon (MBC) and nitrogen (MBN). The LN and MN treatments significantly reduced the MBC and MBN contents (71.6% and 70.8%, 62.5% and 56.8%). Nitrogen application significantly increased the Na+ concentration, with a peak observed under the LN treatment (135.94 mg/kg, p < 0.05). The MN treatment significantly increased the concentrations of Fe3+ and Al3+ (p < 0.05), whereas nitrogen application did not significantly affect Ca2+, Mg2+ concentration, and cation exchange capacity (p > 0.05). Correlation and redundancy analyses (RDAs) revealed that the increase in annual litterfall did not significantly correlate with the rise in POC, and changes in extractable cations were not significantly correlated with the decrease in MAOC. Soil nitrogen availability, MBC, and MBN were identified as the primary factors affecting POC and MAOC content. In conclusion, the application of nitrogen has a detrimental impact on the soil organic carbon (SOC) of Moso bamboo forests. Consequently, it is imperative to regulate fertilization levels in order to preserve soil quality when managing these forests. Our research offers a theoretical foundation for comprehending and forecasting alterations in soil carbon stocks within bamboo forest ecosystems, thereby bolstering the sustainable management of Moso bamboo forests.

[Display omitted] • Mangroves have higher soil OC burial rate, while salt marshes have higher OC stock. • OC from newly established wetland plants is stored unprotected as particulate OC. • Microbially-transformed OC from previous plant community is more mineral-associated. • Oxidizing rhizosphere enhances the association of recent-plant OC with reactive iron. • The formation of reactive iron-associated OC may be inhibited in R. mangle habitats. The global warming-driven poleward expansion of mangrove habitats (e.g., Avicennia germinans and Rhizophora mangle) into temperate salt marshes (e.g., Spartina alterniflora and Juncus roemerianus) has been shown to alter coastal soil organic carbon (SOC) storage. However, the taxa-specific consequences of this vegetation shift on the origin and size of SOC sub-fractions (particulate OC (POC); mineral-associated OC (MAOC); and reactive iron-associated OC (FeR-MAOC)) remain largely unexplored. In this study, we used a particle size-based SOC fractionation method to compare quantity and δ13C composition of bulk and each SOC sub-fractions in soil cores collected from Apalachicola Bay barrier islands in Florida, USA, the highest latitude where monospecific communities of all four aforementioned plants co-occur. Depth-dependent variation of bulk soil δ13C clearly showed the global warming-driven replacement of S. alterniflora by mangroves, as well as reciprocal substitutions of S. alterniflora and J. roemerianus , probably driven by changes in wetland elevation. Higher OC burial rates in mangrove habitats suggested that mangrove soils were principally developed by particle deposition. In contrast, comparatively lower OC burial rates but higher OC stocks in salt marsh habitats illustrated subsurface OC input from salt marsh roots. POC was primarily derived from contemporary plant detritus; its concentration was higher in salt marsh habitats (58.8 ± 9.0 % of SOC) relative to mangroves (38.4 ± 6.0 % of SOC). In contrast, MAOC content did not vary across plant habitats (53.5 ± 10.9 % of SOC), and principally originated from microbially-transformed OC and pre-existing plants. FeR-MAOC was essentially absent in R. mangle soils (2.9 ± 3.6 % of SOC) while representing a minor fraction of MAOC in three other plant habitats (7.8 ± 7.0 % of SOC). The δ13C of FeR-MAOC was more like the present-day surface plants, highlighting the in situ FeR-MAOC formation in their active oxidizing rhizospheres. [ABSTRACT FROM AUTHOR]

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Background: Improvements in farmland soil organic carbon (SOC) stock enhance crop yield and soil fertility while mitigating climate change. Rational fertilization in agricultural production is crucial for safeguarding SOC stock. In this study, field experiments were conducted with different ratios of chemical fertilizer reduction and organic fertilizer substitution for three consecutive years (2018-2020) to explore their effects and interlinkages on SOC fractions, soil properties and SOC stock., Results: The results showed that organic fertilizer substitution increased SOC and its fractions content, SOC stock (by 3.98-12.98% and 7.15-18.13%) and soil fertility index (by 11.76-49.26% and 33.33-91.47%) compared to conventional fertilization in 2019 and 2020, while chemical fertilizer reduction had the opposite effect. Moreover, soil properties (except total nitrogen to total phosphorus ratio, N/P) and SOC fractions significantly affected SOC stock, with SOC fractions contributing more than soil properties. The high sensitivity of microbial biomass carbon (MBC) and dissolved organic carbon (DOC) can indicate changes in soil carbon pool. Structural equation modeling (SEM) revealed that organic fertilizer substitution increased SOC content and stock by increasing SOC fractions [recalcitrant organic carbon (ROC) and labile organic carbon (LOC) fractions] content and soil fertility., Conclusions: Our study revealed the corresponding mechanisms of the two fertilization modes affecting SOC stock changes. The use of organic fertilizer substitution is recommended to increase SOC stocks and soil fertility in wheat fields. © 2023 Society of Chemical Industry., (© 2023 Society of Chemical Industry.)

The conversion of croplands to plantations has been broadly implemented to mitigate climate change. This mitigation effect has been achieved mainly via the sequestration of CO2 from the atmosphere and the storage of carbon within tree biomass and the soil, but this effect is not fully understood. To study this mitigation effect, a poplar plantation, a metasequoia plantation, and a poplar and metasequoia agroforestry system converted from croplands were studied. As such, we investigated the soil nutrient contents, soil organic carbon (SOC) fractions and SOC stocks in the three types of plantations to a depth of 100 cm. High total nitrogen, ammonium-nitrogen, and nitrate-nitrogen contents along the soil profile were detected in the poplar-based plantations. After 10 years of development, the poplar plantation had the greatest SOC fraction contents. The SOC stocks of the poplar plantation and poplar and metasequoia agroforestry system reached 90.35 Mg ha−1 and 98.12 Mg ha−1, respectively. The 0–10, 10–20, and 20–40 cm soil layers accounted for a greater share of the SOC stock in the metasequoia plantation than in the other plantations, and the largest proportion of SOC stock in the poplar and metasequoia system was detected in the subsoil layers. Overall, the different afforestation practices resulted in different SOC accumulation patterns among soil depths, especially in the subsoil. The proportion of the SOC stock in the subsoil layers was greater in the agroforestry plantation than in the pure plantations.

• Facility lands were considered to be greater carbon sinks compared to other land uses. • The most stable type of organic carbon is in facility land, and the most unstable is in grasslands. • Changes in land use have a significant impact on organic carbon fractions and carbon mineralization. Soil carbon is an essential component that influences soil health and agronomic productivity, and land-use practices significantly impact soil carbon stocks. In this study, the researchers investigated the impact of various land-use types (farmland, orchards, grasslands, and facility lands) on soil organic carbon (SOC) fractions in the Qaidam Basin of China's Qinghai-Tibet Plateau. The soil samples were taken from the 0–10 and 10–20 cm depths. The particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) fractions of various land uses have been measured. The results revealed that grasslands had the greatest POC/SOC ratio (0.59), with POC accounting for the majority of the SOC fraction. In contrast, all other land-use types (facility land, orchards, and farmland) had greater MAOC/SOC ratios than POC/SOC. The facility land had the highest SOC content (17.75 g kg−1), and orchard had the lowest (8.51 g kg−1). The grassland had the highest POC content (9.82 g kg−1) at a depth of 0–10 cm. The trend for MAOC content among the various land-use types was facility lands > farmlands > grasslands > orchards. The soil pH was also observed to be moderately alkaline, with an average of 8. The orchard has the highest bulk density (BD), measuring 1.38 g cm−3. The grasslands contained the highest amount of total nitrogen (TN) (2.2 g kg−1) while the agricultural fields contained the highest amount of total phosphorus (TP) (1.16 g kg−1). In addition, facility lands showed the highest level of microbial activity compared to other land-use types. According to the findings, SOC, POC, and MAOC fractions had considerably positive associations with TN and microbial biomass carbon (MBC), but were significantly negatively associated with metabolic CO 2. The findings imply that different land-use types can have a considerable impact on the quality and amount of soil organic carbon, which has consequences for soil health and ecosystem processes. The findings also highlight the significance of long-term land management practices that promote the preservation and enhancement of soil organic carbon in various land-use systems. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) is the largest reservoir of organic carbon in the terrestrial ecosystem, and is an effective mean of enhancing crop production in the irrigated area of the arid and semi-arid regions. Understanding long-term changes in composition of SOM under irrigation from sediment-laden Yellow River water is essential to manage sustainability issues in the agro-ecosystem. A total of 45 soils, including 39 of irrigated fields differing in irrigation history and 6 of non-cultivated and non-irrigated natural fields as the control, were sampled at 0–20 cm depth. The soil was analyzed for total SOC content, partitioning of light (LFOM) and heavy (HFOM) fraction organic matter based on NaI solution density of 1.7 g m 3 and for particle size distribution. Compared to the non-irrigated and non-cultivated control soil, the LFOM and HFOM in irrigated soils increased with the duration of irrigation though SOM existed dominantly as the heavy fraction. The soils irrigated for <50 years have overall lesser LFOM and HFOM and more sand compared to those with >50 years irrigation. Further, a positive relationship existed between the fine particle and the SOM or its fractions (negative relation with coarse particle) suggesting either SOM accumulated as fine particles or the fine mineral particles better preserved SOM. In addition, field soil moisture at the time of sampling during October 2009 correlated with HFOM ( p  < 0.001) and LFOM ( p  < 0.01). The study suggested that the long-term irrigation with water diverted from Yellow River increased fine particle, SOC and the light and heavy fraction in the Ningxia Irrigation Zone. [ABSTRACT FROM AUTHOR]

Charcoal is a carbonaceous particulate matter with a highly aromatic structure produced by incomplete combustion, and it can cause persistent long-term effects on soil ecological functions. In this study, we determined soil organic carbon pools and associated enzyme activities following five years of different charcoal treatments[charcoal removal (B 0 ), charcoal retained in situ (B 1 ), and the addition of charcoal removed from B 0 (B 2 )] and the unburnt control (UB) in a recently harvested Pinus massoniana plantation subjected to broadcast burning. The results showed that dissolved organic carbon (DOC), microbial biomass carbon (MBC), coarse and fine particulate organic carbon (CPOC and FPOC), and recalcitrant carbon (RC) contents were significantly lower in B 1 than those in UB soil ( P <0.05). The MBC and FPOC contents of B 2 soil were comparable to those of UB soil, which were significantly higher than those of B 0 soil ( P <0.001). There was no difference in MBC/TC between the B 2 and UB soils, whereas MBC/TC was significantly lower in B 0 than in UB soil ( P <0.05). β -glucosidase and peroxidase activities of B 0 , B 1 , and B 2 soils were significantly lower than that of UB soil ( P <0.01), and polyphenol oxidase activity was significantly lower in B 0 and B 2 soils than in UB soil ( P <0.01). No significant difference in soil TC, DOC, readily oxidized carbon (ROC), CPOC, and RC content as well as associated enzyme activities was observed among the charcoal treatments ( P >0.05). Redundancy analysis showed that sucrose and polyphenol oxidase were the key drivers influencing soil organic carbon fractions, accounting for 16.3% and 12.7% of the total variance, respectively. Overall, our findings indicated that fire-deposited charcoal played a positive role in enhancing soil microbial biomass carbon recovery, soil organic carbon accumulation, and stability, highlighting the importance of charcoal in the management of subtropical plantations in the future.

Purpose: A large body of research suggests that rice ( Oryza sativa L.) cropping facilitates soil organic carbon (SOC) storage, while the stability of the sequestered carbon is still not well understood. The objective of this study was to determine the differences in SOC stocks and fraction distributions between rice paddies and upland cropping fields and their variation in different rice cropping areas. Materials and methods: Data from the national soil survey were analyzed to assess the differences in SOC contents between paddy and upland cropping fields at the regional scale. In addition, three pairs of rice and upland cropping systems were selected in Heilongjiang [single rice vs. single corn ( Zea mays L.) cropping], Jiangsu [rice-wheat ( Triticum aestivum L.) vs. corn-wheat cropping], and Jiangxi (double rice vs. double corn cropping) provinces, representing the major cropping patterns in China. Physical fractionation techniques were used to investigate the differences in SOC stocks and distribution among different pools between rice-based cropping systems and non-rice cropping systems in China. Results and discussion: SOC concentrations were, on average, 74.9% higher at the regional scale and 56.8% higher at the field scale in paddy than in upland cropping fields. Carbon proportion of particulate organic matter within microaggregates increased from 14.4% in upland cropping soils to 25.3% in paddy soils at the Heilongjiang site and from 12.4 to 25.5% at the Jiangxi site. Meanwhile, the free silt and clay-associated carbon was significantly greater in paddy than in upland cropping soils at the both sites. Nevertheless, SOC distribution did not markedly differ between paddy and upland cropping fields at the Jiangsu site where rice was rotated with winter wheat annually. Conclusions: As compared to upland cropping or rice-upland crop rotation, continuous rice cropping, such as single and double rice cropping, could favor SOC stabilization by occlusion within microaggregates and adsorption to the silt and clay outside microaggregates, which may promote the long-term storage of SOC in paddies. [ABSTRACT FROM AUTHOR]

Abstract: Soil organic carbon (SOC) has an important role in improving soil quality and sustainable production. A long-term fertilization study was conducted to investigate changes in SOC and its relation to soil physical properties in a rice paddy soil. The paddy soils analyzed were subjected to different fertilization practices: continuous application of inorganic fertilizers (NPK, N–P–K=120–34.9–66.7kgha−1 yr−1 during 1967–1972 and 150–43.7–83.3kgha−1 yr−1 from 1973 to 2007), straw based compost (Compost, 10Mgha−1 yr−1), a combination of NPK+Compost, and no fertilization (control). Soil physical properties were investigated at rice harvesting stage in the 41st year for analyzing the relationship with SOC fraction. Continuous compost application increased the total SOC concentration in plough layers and improved soil physical properties. In contrast, inorganic or no fertilization markedly decreased SOC concentration resulting to a deterioration of soil physical health. Most of the SOC was the organo-mineral fraction (<0.053mm size), accounting for over 70% of total SOC. Macro-aggregate SOC fraction (2–0.25mm size), which is used as an indicator of soil quality rather than total SOC, covered 8–17% of total SOC. These two SOC fractions accumulated with the same tendency as the total SOC changes. Comparatively, micro-aggregate SOC (0.25–0.053mm size), which has high correlation with physical properties, significantly decreased with time, irrespective of the inorganic fertilizers or compost application, but the mechanism of decrease is not clear. Conclusively, compost increased total SOC content and effective SOC fraction, thereby improving soil physical properties and sustaining production. [Copyright &y& Elsevier]

Vegetation restoration has been proposed as an effective strategy for increasing soil organic carbon (SOC) sequestration. However, the responses of SOC to managed and natural vegetation restoration strategies at a large scale are poorly understood due to the varying SOC components and changing climatic conditions. Here, we measured bulk SOC, particulate organic carbon (POC), and mineral-associated organic carbon (MOC) after 15 years of vegetation restoration along an elevation gradient with a corresponding temperature gradient in the calcareous soils of karst region, Southwest China. We compared managed plantation forest and naturally recovered shrubland vegetation restoration strategies, using cropland and mature forest as references. Overall, we found that the SOC and POC densities in both plantation forest and shrubland were significantly higher than in the cropland but lower than in the mature forest. There were no significant differences in the SOC pool between the plantation forest and shrubland. Furthermore, the relative changes in the SOC and POC densities increased with increasing mean annual temperature in the plantation forest and shrubland. Our results showed that both vegetation restoration strategies, characterized by higher soil microbial abundance and exchangeable Ca concentration, were beneficial to POC but not MOC accumulation, and sufficiently compensated SOC decomposition at lower elevation with higher MAT. Our results highlight the potential of both vegetation restoration strategies for promoting SOC accumulation in warmer karst regions and emphasize the necessity to understand soil carbon stabilization mechanisms in calcareous soils. Unlabelled Image • Managed and natural vegetation restoration were compared along a climatic gradient. • Both vegetation restoration strategies increased soil carbon stocks in warmer regions. • Higher temperature shifted soil microbial community structure. • Restored vegetation had higher microbial abundance and calcium than cropland. • Microbial abundance and calcium negated effect of temperature on SOC decomposition. [ABSTRACT FROM AUTHOR]

Cultivated grassland can serve as one solution to the degradation of natural grassland. However, less is understood of the response of the microbial communities in cultivated grassland soils to global change factors such as nitrogen (N) deposition and precipitation change, and their linkages with the dynamics of soil organic carbon (SOC). In this study, field experimental plots that simulate different N deposition and precipitation levels were established to investigate the responses of soil microbial communities and their linkages with particulate-sized SOC fractions. Results showed that the activities of hydrolytic enzymes responded significantly to N addition, watering and their combinations, whereas the abundance and composition of microbial communities showed no significant difference among treatments. Addition of N and water generally promoted the activities of N-degrading enzymes such as β-N-acetylglucosaminidase (NAG) and leucine aminopeptidase (LAP), and thus decreased the C- to N-degrading activity (enzyme C/N ratio). This decrease in enzyme C/N ratio was significantly correlated with the accumulation of microbial-accessible particulate organic carbon (POC), indicating that three years of N application did not alleviate microbial N limitation so that microbial communities had invested more in acquisition of N instead of C. In contrast, the content of microbial-inaccessible mineral associated organic carbon (MAOC) was decreased probably as a result of N limitation on the suppressed microbial growth. Collectively, these results highlight that stoichiometric deviation between substrate and microbial demand can be one critical driver for SOC dynamics in cultivated grassland under global change scenarios. • Nitrogen addition and watering significantly affected soil enzymatic activity. • The C- to N-degrading activity was decreased by N addition and watering. • Nitrogen addition and watering generally promotes POC but reduces MAOC. • Changes in POC and MAOC were tightly related to alterations in enzyme C:N ratio. [ABSTRACT FROM AUTHOR]