More Microbial Function Than Taxonomic Convergence in Soil Straw Decomposition

Bacteria and fungi are key agents in plant residue decomposition, and their roles are determined by their taxonomic and functional compositions. However, the spatiotemporal patterns of microbial diversity, particularly functional traits, remain poorly understood. To close this gap, we conducted a 16-week field-based rice straw burial experiment coupled with amplicon sequencing. Random forest (RF) analysis revealed that soil chemical properties (available potassium (AK), pH, and soil organic matter (SOM)) and climate factors (MAP and MAT) were the main predictors of bacterial and fungal taxonomic composition, explaining 46.9% and 27.3% of the variation, respectively. In contrast, the functional composition related to straw decomposition was less influenced, with these factors explaining 0% of the variation for bacteria and 31.4% for fungi. The distance–decay relationship (DDR) model further showed significant spatiotemporal differences in the taxonomic composition between straw-decomposing fungi and bacteria, with fungi exhibiting greater variability, as indicated by a steeper slope (−2E−04) than that for bacteria (−9E−05). However, the functional composition related to straw decomposition showed no significant spatiotemporal variation. Our results demonstrate that the taxonomic variability of straw-degrading bacteria and fungi is shaped by distinct environmental factors, whereas their functional composition remains stable across space and time, reflecting functional redundancy in terms of straw decomposition.