• Straw returning significantly affects silicon fraction transformation;

Returning crop straw into the soil is an important practice to balance biogenic and bioavailable silicon (Si) pool in paddy, which is crucial for the healthy growth of rice. However, owing to little knowledge about soil microbial communities responsible for straw degradation, how straw return affects Si bioavailability, its uptake, and rice yield remains elusive. Herein, we investigate the change of soil Si fractions and microbial community in a 39-year-old paddy field amended by a long-term straw return. Results show that rice straw return significantly increased soil bioavailable Si and rice yield from 29.9% to 61.6% and from 14.5% to 23.6%, respectively, when compared to NPK fertilization alone. Straw return significantly altered soil microbial community abundance. Acidobacteria was positively and significantly related to amorphous Si, while Rokubacteria at phylum level, Deltaproteobacteria, and Holophagae at class level was negatively and significantly related to organic matter adsorbed and Fe/Mn-oxide-combined Si in soils. Redundancy analysis of their correlations further demonstrated that Si status significantly explained 12% of soil bacterial community variation. These findings suggest that soil bacteria community and diversity interact with Si mobility by altering its transformation, thus resulting in the balance of various nutrient sources to drive biological Si cycle in agroecosystem.