Adaptation and assembly of microbial communities under saline-alkaline stress in paddy ecosystems: Implications for nitrogen and carbon cycling

Abstract

Rice cultivation is a pivotal strategy in mitigating soil salinity. Nitrogen (N) is an essential mineral element in food production, while carbon (C) serves as the primary structural element of organic matter in food. However, the potential microbiological mechanisms underlying C and N transformation under different saline-alkali conditions remain unclear. This study investigated dynamic changes of N and C in high (H), medium (M), and low (L) saline-alkali paddy soils, and quantified the assembly processes of microbial communities. Post-harvest, H exhibited higher levels of nitrous-N, nitrate-N, and total-N compared to L. Total organic-C increased with the duration of rice growth, with H showing the largest gain (83 %) after harvest relative to pre-planting. The ecological filtration effect resulting from elevated salinity-alkalinity decreased species diversity of the community, whereas the relative abundance of key functional microbial groups engaged in C and N metabolism exhibited a positive response, demonstrating a persistent advantage in environmental adaptation. Null model analysis showed that saline-alkaline stress sharply reduced homogeneous selection but increased homogenizing dispersal. As salinity-alkalinity intensified, drift declined while diffusion limitation became more prominent, suggesting that physical barriers to microbial migration are more prominent in salinity-alkalinity habitats. Such barriers may enhance the likelihood of critical ecosystem functions being maintained through either “complementary effects” or functional redundancy within microbial groups. These distinct contributing groups imply contributes to the formation of soil organic-C pools. These results clarify the mechanisms driving biotic community assembly and ecosystem regulation under intensified saline-alkaline stress.

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