Junhui Chen

Liming is widely used to alleviate soil acidification, but its potential to stimulate soil organic carbon (SOC) decomposition may compromise SOC stability. Whether lime–biochar co-application can mitigate the associated increase in soil CO₂ release remains unclear. A one-year field experiment in an intensively managed acid bamboo plantation compared an unamended control (CK), lime alone (L), bamboo biochar alone (B), and lime–biochar co-application (LB). Soils collected at 3, 6, and 12 months after application were analyzed for SOC fractions, extracellular enzyme activities, and microbial gene abundance and incubated for 90 days to measure CO₂ release. At 3 and 6 months, L increased cumulative CO₂-C release by 45% and 24%, respectively, relative to CK, accompanied by increased labile C and microbial C limitation inferred from enzyme stoichiometry. Relative to L, LB reduced mean CO₂-C release rates by 18% and 13%, respectively; this response was associated with higher non-hydrolysable (recalcitrant) C, lower geometric mean enzyme activity, and weaker microbial C limitation. After 12 months, the stimulatory effect of L was no longer evident, whereas B and LB increased cumulative CO₂-C release by 31% and 29%, respectively, relative to CK. Structural equation modeling linked the lime predictor to greater microbial abundance and C limitation, and the biochar predictor to higher recalcitrant C concentrations and lower C limitation. Because CO₂ sources were not partitioned, these responses cannot be attributed exclusively to native SOC decomposition. Lime–biochar co-application thus moderated the short-term increase in soil CO₂ release associated with liming, but this effect weakened over time, highlighting the need for longer-term assessment of SOC stability.

Optimizing nitrogen (N) management is essential for sustaining rice productivity and improving soil N retention in paddy ecosystems, yet whether long-term fertilizer postponing (FP) regulates bacterial community assembly and microbial N-cycling potential in a compartment-dependent manner remains unclear. Using soils from an 11-year field experiment, we investigated bacterial communities and eight N-cycling genes in bulk and rhizosphere soils across three rice growth stages. Compared with conventional fertilization (CF), FP significantly increased grain yield, plant N accumulation, soil NH₄⁺-N (8.1%), microbial biomass N (MBN, 4.3%), and urease activity (30.3%). N-cycling genes showed pronounced temporal variation, generally peaking at the heading stage. FP increased the abundance of genes involved in N fixation, nitrification, and denitrification in bulk soil but reduced most N-cycling genes in the rhizosphere. Although bacterial α-diversity was unchanged, FP significantly altered bacterial community composition. Network and redundancy analysis further showed that bacterial community assembly and N-cycling potential were closely associated with soil C and N status. These findings indicate that long-term FP improves rice productivity by enhancing soil N availability and reshaping bacterial community assembly and microbial N-cycling potential in a compartment-dependent manner, providing new insights into the microbial mechanisms underlying sustainable N management in paddy soils.

Mitigating methane (CH₄) emissions from paddy fields without compromising yield remains a critical challenge for sustainable agriculture, primarily due to trade-offs between emission reduction and nutrient availability. Biochar-based fertilizer (BF), which integrates biochar with mineral nutrients, may address this constraint by regulating carbon and nitrogen availability. This study evaluated the effects of biochar-based fertilization on CH₄ emissions and rice productivity. A one-season field experiment was conducted in Hydragric Anthrosols with four treatments: no fertilization (control), conventional chemical fertilization (CF), integrated application of biochar-based and chemical fertilizers (CBF), and biochar-based fertilizer alone (BF). Methane fluxes were monitored alongside soil physicochemical properties and the abundances of key functional microbial genes. Compared with CF, BF significantly reduced cumulative CH₄ emissions by 23.24% while maintaining comparable rice yield, resulting in a 28.67% reduction in yield-scaled CH₄ emissions. Biochar-based fertilization decreased dissolved organic carbon availability, buffered NH₄⁺-N concentrations, and increased soil pH. These changes shifted the microbial balance of CH₄ cycling, suppressing methanogenesis and enhancing methane oxidation, as reflected by a lower mcrA/pmoA ratio. Structural equation modeling indicated that CH₄ mitigation was jointly driven by reduced methanogenic activity and enhanced methane oxidation. Overall, biochar-based fertilization regulates soil chemical and microbial processes to mitigate CH₄ emissions without yield penalties, demonstrating strong potential as a scalable and field-applicable strategy for low-carbon rice production.

Both biochar and oyster shell powder have been known as promising amendments to ameliorate soil acidity and enhance soil fertility. However, it is still unclear how their application alone and in combination affect the soil organic carbon (C) fraction and microbial activity in subtropical bamboo plantations. Therefore, to investigate the effects of biochar and oyster shell powder on soil microbial respiration, organic C fractions, microbial biomass, and enzyme activities related to C, N and P cycling, topsoil samples were collected from plots in a bamboo (Phyllostachys praecox) plantation that has been amended with oyster shell powder at 4 t ha⁻¹ (T), bamboo biochar at 10 t ha⁻¹ (B), and their combination (TB, with 4 t ha⁻¹ T and 10 t ha⁻¹ B) for 8 months. Our results showed that T alone significantly increased soil microbial respiration by 21.5%, whereas B alone and TB significantly decreased soil microbial respiration and metabolic quotient compared with T. T alone also increased soil pH, the size of labile C pool and the activities of β−glucosidase and cellobiosidase, whereas TB rather than B increased soil pH, the recalcitrant C pool size and declined these enzyme activities relative to T. T alone significantly enhanced microbial C limitation by 28.6% and decreased P limitation by 13.0%, while TB decreased microbial C limitation and increased microbial C use efficiency (CUE). Structural equation modeling indicated that T enhanced soil microbial respiration through increasing soil pH and enzyme activity, while biochar co-addition weakened the stimulation of T on microbial respiration by increasing soil recalcitrant C pool size and microbial metabolic quotient. Our study suggests that adding bamboo biochar together with oyster shell powder could be a better strategy to decrease soil C loss and ameliorate soil acidity in bamboo plantations compared with the application of oyster shell powder alone.