The divergent response of fungal and bacterial necromass carbon in soil aggregates under biochar amendment in paddy soil

Abstract

Background and aims

Microbial necromass carbon (C) significantly contributes to soil organic carbon (SOC) sequestration. However, there is limited information on how biochar amendment affects the accumulation and allocation of microbial necromass C in soil aggregates in paddy soil remains scarce, particularly with regard to changes in microbial life strategies.

Methods

From a 2-year field experiment, topsoil samples with biochar (C15) and without biochar amendment (C0) treatments were collected and fractionated into macroaggregate (2000–250 μm), microaggregate (250–53 μm), and silt–clay (< 53 μm) fractions. We investigated the impact of maize straw-derived biochar amendment on microbial community structure, SOC, and microbial necromass C in paddy soil aggregates.

Results

Biochar amendment significantly increased SOC and microbial biomass C but reduced microbial necromass C concentration. The microbial community shifted towards K-strategists under biochar amendment. Compared with the C0 treatment, total necromass C concentration in the C15 treatment decreased by 14.9% in the bulk soil, primarily due to reductions in fungal and bacterial necromass C concentrations of 14.7% and 16.1%, respectively. The decrease in total necromass C was primarily observed in macroaggregate and microaggregate. Specially, fungal necromass C primarily decreased in macroaggregate, while bacterial necromass C decreased in microaggregate. Biochar amendment did not significantly reduce microbial necromass C in silt–clay fraction, indicating its greater stabilization due to strong binding with soil minerals under biochar amendment, thereby protects it from microbial decomposition.

Conclusions

The results offer new insights into the role of soil aggregates in microbial-mediated SOC sequestration following biochar amendment in paddy soil.