Long-term cultivation reduces soil carbon storage by altering microbial network complexity and metabolism activity in macroaggregates

Cultivation alters soil aggregation, microbial compositions and the potential for carbon sequestration in cropland soils. However, the specific effects of long-term cultivation and the underlying mechanisms on soil organic carbon (SOC) storage at different aggregate sizes remain poorly understood. We characterized the dynamics of SOC storage in macroaggregates (>0.25 mm) and microaggregates (<0.25 mm) across four paddy soils successively cultivated for 60, 100, 125, and 150 years. Microbial community compositions, network patterns, enzyme activities and carbon use efficiency (CUE) were examined to elucidate the underlying microbial pathways governing SOC storage. The results showed that prolonged cultivation led to an average reduction of 45 % in SOC storage, particularly in macroaggregates. Partial least squares path modeling revealed that shifts in microorganisms in macroaggregates explained almost 80 % of the variation in SOC storage. Specifically, variations in fungal composition and decreased complexity of microbial interaction networks were strongly correlated with SOC storage. Fungal community and microbial interactions also indirectly affected SOC storage by positively correlating with extracellular enzyme activity. Moreover, bacterial composition indirectly regulated SOC storage by positively correlating with carbon use efficiency. Our findings indicated that the macroaggregate-associated microbial interactions and the metabolism activities had significant implications for SOC sequestration in paddy fields. We suggest that implementation of management practices targeted at improvement of these microbial attributes could enhance agroecosystems sustainability.