Explore the vast range of titles available.

Soil microbial necromass plays a critical role in soil organic C (SOC) sequestration, while the long-term response of microbial necromass to climate change remains largely unclear. Here, we used amino sugars as biomarkers and examined their variation after 8 years of continuous manipulation of elevated CO2 (eCO2), warming, and their combined interaction in a paddy soil. Our results showed that eCO2 increased the concentrations of all amino sugar compounds by 6.5–28.9% while warming had no effect on the accumulation of glucosamine and galactosamine but increased muramic acid concentration by 22.1–29.1%. Elevated CO2 increased the contribution of microbial necromass C to SOC storage, mainly by increasing fungal-derived C, whereas warming increased the bacterial-derived C proportion in SOC. Furthermore, the combined effect of eCO2 and warming yielded the highest total microbial necromass and SOC accumulation, although the ratio of fungal to bacterial necromass C in SOC remained unchanged. Structural equation models showed that root biomass had an indirect positive effect on total amino sugar concentration, mainly through increased microbial biomass, whereas N-acetylglucosaminidase activity had a direct negative effect on total amino sugar accumulation. These differential responses of microbial necromass to climate change may further alter the sequestration of SOC. This study is only based on one sampling time, and future research should involve more sampling times so as to have the temporal dynamics of the studied properties. Our findings emphasize the contribution of the microbial-derived C to soil C stock under long-term elevated CO2 and warming in a rice-wheat rotation system, which reveals an important mechanism of microbial-mediated C sequestration under climate change.

As one of the most important nutrients for plant growth, phosphorus was often poorly available in soil. While biochar addition induced improvement of soil structure, nutrient and water retention as well as microbial activity had been well known, and the effect of biochar soil amendment (BSA) on soil phosphorus availability and plant P uptake had been not yet quantitatively assessed. In a review study, data were retrieved from 354 peer-reviewed research articles on soil available P content and P uptake under BSA published by February 2019. Then a database was established of 516 data pairs from 86 studies with and without BSA in agricultural soils. Subsequently, the effect size of biochar application was quantified relative to no application and assessed in terms of biochar conditions, soil conditions, as well as experiment conditions. In grand mean, there was a significant and great effect of BSA on soil available P and plant P uptake by 65% and 55%, respectively. The effects were generally significant under manure biochar, biochar pyrolyzed under 300 °C, soil pH <5 and fine-textured soil, and soils that are very low in available P. Being significantly correlated to soil P availability ( R 2 =0.29), plant P uptake was mostly enhanced with vegetable crops of high biomass yield. Overall, biochar amendment at a dosage up to 10 t ha −1 could be a tool to enhance soil availability and plant uptake of phosphorus, particularly in acid, heavy textured P-poor soils.

A field experiment was conducted in a Cd-contaminated rice paddy field to evaluate the effect of inorganic and organic metal stabilizers on Cd mobility and rice uptake. A dose of inorganic stabilizer of calcium hydroxide (CH), silicon slag (SS), and wheat straw biochar (BC) was amended respectively to topsoil before rice transplanting. Rice production was managed with the same water regime and fertilization practices consistently between treatments including a control without amendment. Samples of topsoil and rice plant were collected at rice harvest to analyze the Cd mobility and uptake by rice. Without affecting rice grain yield, the stabilizers significantly decreased CaCl 2 -extractable Cd in a range of 44 to 75 % compared to the control, corresponding to soil pH changes under the different treatments. Accordingly, Cd concentrations both in rice tissue and in rice grain were very significantly decreased under these treatments. The decrease in rice Cd uptake was correlated to the decrease in extractable Cd, which was again correlated to soil pH change under the different treatments, indicating a prevalent role of liming effect by the amendments. While applied at a large amount in a single year, organic stabilizer of BC decreased Cd extractability by up to 43 % and Cd rice uptake by up to 61 %, being the most effective on Cd immobilization. However, the long-term effect on soil health and potential tradeoff effects with different stabilizers deserve further field monitoring studies.

Upland fields are a significant source of N2O emissions. Thus, an accurate estimation of these emissions is essential. This study employed four classical modeling approaches—the Stepwise Regression Model, Decision Tree Regression, Support Vector Machine, and Random Forest (RF)—to simulate soil N2O emissions from Chinese upland fields. The upland crops considered in this study covered food crops, oil crops, cash crops, sugar crops, fruits, and vegetables, excluding flooded rice. Comparative analysis revealed that the RF algorithm performed the best, with the highest R2 at 0.66 and the lowest root mean square error at 0.008 kg N2O ha−1 day−1. The application rate of mineral nitrogen fertilizers, mean temperature during the growing season, and soil organic carbon content were the key driving factors in the N2O emission model. Utilizing the RF model, total N2O emissions from Chinese upland fields in 2020 were estimated at 183 Gg. Future projections under Representative Concentration Pathway (RCP) scenarios indicated a 2.80–5.92% increase in national N2O emissions by 2050 compared to 2020. The scenario analysis demonstrated that the proposed nitrogen reduction strategies fail to counteract climate-driven emission amplification. Under the combined scenarios of RCP8.5 and nitrogen reduction strategies, a net 4% increase in national N2O emissions was projected, highlighting the complex interplay between anthropogenic interventions and climate feedback mechanisms. This study proposes that future attention should be paid to the development of nitrogen optimization strategies under the impact of climate change.

While biochar soil amendment has been widely proposed as a soil organic carbon (SOC) sequestration strategy to mitigate detrimental climate changes in global agriculture, the SOC sequestration was still not clearly understood for the different effects of fresh and aged biochar on SOC mineralization. In the present study of a two‐factorial experiment, topsoil samples from a rice paddy were laboratory‐incubated with and without fresh or aged biochar pyrolyzed of wheat residue and with and without crop residue‐derived dissolved organic matter (CRM) for monitoring soil organic matter decomposition under controlled conditions. The six treatments included soil with no biochar, with fresh biochar and with aged biochar treated with CRM, respectively. For fresh biochar treatment, the topsoil of a same rice paddy was amended with wheat biochar directly from a pyrolysis wheat straw, the soil with aged biochar was collected from the same soil 6 years following a single amendment of same biochar. Total CO2 emission from the soil was monitored over a 64 day time span of laboratory incubation, while microbial biomass carbon and phospholipid fatty acid (PLFA) were determined at the end of incubation period. Without CRM, total organic carbon mineralization was significantly decreased by 38.8% with aged biochar but increased by 28.9% with fresh biochar, compared to no biochar. With CRM, however, the significantly highest net carbon mineralization occurred in the soil without biochar compared to the biochar‐amended soil. Compared to aged biochar, fresh biochar addition significantly increased the total PLFA concentration by 20.3%–33.8% and altered the microbial community structure by increasing 17:1ω8c (Gram‐negative bacteria) and i17:0 (Gram‐positive bacteria) mole percentages and by decreasing the ratio of fungi/bacteria. Furthermore, biochar amendment significantly lowered the metabolic quotient of SOC decomposition, thereby becoming greater with aged biochar than with fresh biochar. The finding here suggests that biochar amendment could improve carbon utilization efficiency by soil microbial community and SOC sequestration potential in paddy soil can be enhanced by the presence of biochar in soil over the long run. This work aimed to compare the effect of short‐term and long‐term biochar amendment on soil organic carbon (SOC) sequestration potential. Topsoil samples from a rice paddy were incubated with and without fresh or aged biochar and with and without crop residue‐derived dissolved organic matter for monitoring soil organic matter decomposition under controlled conditions. Furthermore, microbial biomass carbon and phospholipid fatty acid were determined at the end of incubation period. The finding suggests that biochar amendment could improve carbon utilization efficiency and SOC sequestration potential can be enhanced in paddy soil by the presence of biochar over the long run.

Denitrification is one of the most important soil microbial processes leading to the production of nitrous oxide (N 2 O). The potential changes with metal pollution in soil microbial community for N 2 O production and reduction are not well addressed. In this study, topsoil samples were collected both from polluted and non-polluted rice paddy fields and denitrifier communities were characterized with molecular fingerprinting procedures. All the retrieved nirK sequences could be grouped into neither α- nor β- proteobacteria , while most of the nosZ sequences were affiliated with α- proteobacteria . The abundances of the nirK and nosZ genes were reduced significantly in the two polluted soils. Thus, metal pollution markedly affected composition of both nirK and nosZ denitrifiers. While the total denitrifying activity and N 2 O production rate were both reduced under heavy metal pollution of the two sites, the N 2 O reduction rate showed no significant change. These findings suggest that N 2 O production activity could be sensitive to heavy metal pollution, which could potentially lead to a decrease in N 2 O emission in polluted paddies. Therefore, metal pollution could have potential impacts on soil N transformation and thus on N 2 O emission from paddy soils.

While high soil carbon stability had been well known for biochar‐amended soils, how conversion of crop residues into biochar and subsequent biochar amendment (BA) would favor microbial carbon use and carbon sequestration had not been clearly understood. In this study, topsoil samples were collected from an upland soil and a paddy soil, both previously amended with straw and straw‐derived biochar. These samples were incubated with 13C‐labeled maize residue (LMR) for 140 days to compare carbon mineralization, metabolic quotient (qCO2), and microbial carbon use efficiency (CUE) under laboratory incubation. 13C‐phospholipid fatty acid (13C‐PLFA) was used to trace the use of substrate carbon by soil microorganisms. Comparing to straw amendment (SA), BA significantly decreased the native soil organic carbon (SOC) mineralization rates by 19.7%–20.1% and 9.2%–12.0% in the upland and paddy soils, respectively. Meanwhile, total carbon mineralization from the newly added LMR was significantly decreased by 12.9% and 11.1% in the biochar‐amended soils, compared with the straw‐amended soils from the upland and paddy sites, respectively. Furthermore, compared to non‐amended soils, the qCO2 value was unchanged in straw‐amended soils, but was notably decreased by 15.2%–18.6% and 8.9%–12.5% in biochar‐amended upland and paddy soils, respectively. Microbial CUE was significantly greater in biochar‐amended soils than in straw‐amended soils due to the increasing dominance of fungi in carbon utilization. Compared to SA, BA increased CUE by 23.0% in the upland soil and 21.2% in the paddy soil. This study suggests that BA could outperform SA in the long term to enhance the biological carbon sequestration potential of both upland and paddy soils. This could be due mainly to biochar input as a special substrate to promote microbial community evolution and increase the fungal utilization of carbon substrates, especially for the soil with lower SOC levels. This work aimed to compare the effect of crop straws and crop straw‐derived biochar amendment (BA) on microbial carbon use and carbon sequestration potential. Topsoil samples were collected from an upland soil and a paddy soil, both previously amended with straw and straw‐derived biochar, and these samples were incubated with 13C‐labelled maize residue to monitor the soil organic matter decomposition. Moreover, the metabolic quotient, microbial carbon use efficiency and 13C‐phospholipid fatty acid were analyzed. This study suggests that BA could outperform straw amendment in the long term to enhance the biological carbon sequestration potential of both upland and paddy soils.

While microbial nitrogen transformations in soils had been known to be affected by heavy metal pollution, changes in abundance and community structure of the mediating microbial populations had been not yet well characterized in polluted rice soils. Here, by using the prevailing molecular fingerprinting and enzyme activity assays and comparisons to adjacent non-polluted soils, we examined changes in the abundance and activity of ammonia oxidizing and denitrifying communities of rice paddies in two sites with different metal accumulation situation under long-term pollution from metal mining and smelter activities. Potential nitrifying activity was significantly reduced in polluted paddies in both sites while potential denitrifying activity reduced only in the soils with high Cu accumulation up to 1300 mg kg-1. Copy numbers of amoA (AOA and AOB genes) were lower in both polluted paddies, following the trend with the enzyme assays, whereas that of nirK was not significantly affected. Analysis of the DGGE profiles revealed a shift in the community structure of AOA, and to a lesser extent, differences in the community structure of AOB and denitrifier between soils from the two sites with different pollution intensity and metal composition. All of the retrieved AOB sequences belonged to the genus Nitrosospira, among which species Cluster 4 appeared more sensitive to metal pollution. In contrast, nirK genes were widely distributed among different bacterial genera that were represented differentially between the polluted and unpolluted paddies. This could suggest either a possible non-specific target of the primers conventionally used in soil study or complex interactions between soil properties and metal contents on the observed community and activity changes, and thus on the N transformation in the polluted rice soils.

Improving nitrogen (N) use efficiency (NUE) in crop plants is important to reduce the negative impact of excessive N on the environment. Although biochar‐blended fertilizer had been increasingly tested in crop production, the fate of fertilized N in soil and plant had not been elucidated in field conditions. In this study, a novel biochar‐blended urea (BU) was prepared by pelleting maize straw biochar, bentonite, sepiolite, carboxymethylcellulose sodium, and chitosan with urea (commercial urea without biochar [CU]). N fertilization in a winter wheat field was treated with BU and CU at both 265 kg N ha−1 (HL) and 186 kg N ha−1 (LN). Within a treatment plot, a microplot was fertilized with 15N‐labeled urea at a relevant N level. We investigated the influence of fertilizer management on biomass, grain yield, bioaccumulation of nutrient, soil properties, 15N isotopic abundance, and greenhouse gas emissions. Microscopic and spectroscopic analysis showed that micro/nanonetwork of biochar could bind N to form a loss control agglomerated particle, and organo‐mineral coatings on BU may protect N from quick release. Compared with CU, BU significantly increased grain yield by 13% and 38%, and grain N allocation by 19% and 55%, respectively, at HN and LN level. The total recovery of urea 15N in wheat plant (15N based NUE) was 32.8% under CU regardless of N rates but increased to 41.7% (HN rate) and 56.3% (LN rate) under BU. Whereas, the soil proportion (soil residual 15N) was 20.1% and 13.4% under CU but 32.5% and 18.8% under BU, in 0‐20cm topsoil, respectively, at HN and LN rate. Compared with the CU, BU had no effect on CO2 and CH4 emissions but significantly reduced the total N2O emission by 23%–28%. These important findings suggested that BU can be beneficial to uplift plant NUE to reduce reactive N loading but boost crop production. Improving nitrogen use efficiency (NUE) in crop plants is important to reduce the negative impact of excessive N on the environment. A novel, biochar‐blended urea (BU) was prepared by pelleting maize straw biochar, bentonite, sepiolite, carboxymethylcellulose sodium, and chitosan with urea. Within a field experiment, a microplot was fertilized with 15N‐labeled urea at two different N levels. We investigated the urea fertilization on wheat biomass, yield, bioaccumulation of nutrient, soil properties, 15N isotopic abundance, and greenhouse gas emissions. The findings indicated that BU can be beneficial to increase plant NUE to reduce reactive N loading but boost crop production.

Soil amendment with biochar is being promoted as a promising strategy for carbon (C) stabilization and accrual, which are key to climate change mitigation. However, it remains elusive on how biochar addition influences nonbiochar C in soils and its mechanisms, especially in the presence of plants. Here we conducted a 365-day soil microcosm experiment with and without adding 13 C-labeled biochar into topsoil to quantify changes in nonbiochar C in the topsoil and subsoil in the presence or absence of rice plants and to determine the mechanisms by which biochar controls nonbiochar C accrual in the soil profile. The nonbiochar C content of topsoil was not affected by biochar addition in the absence of rice plants, but was significantly increased by 4.5% in the presence of rice plants, which could result from increases in the soil macroaggregate fraction, iron (Fe)-bound nonbiochar organic C content, and fungal biomass collectively. However, biochar amendment had no effect on the content of nonbiochar organic C in the subsoil. Overall, biochar-plant interactions drive more nonbiochar C sequestration in the topsoil, and the changes of nonbiochar C in planted soils following biochar addition should be quantified to better assess the soil C sequestration potential in agricultural lands.