Effects of continuous straw returning on bacterial community structure and enzyme activities in rape-rice soil aggregates

This study investigated the effects of straw returning on the bacterial community and enzyme activities of soil aggregates. A five-year field trial was carried out in a paddy soil with three treatments: no straw + no fertilization (CK), compound fertilizer (F), and straw returning + compound fertilizer (SF). Soil aggregates were classified into mega-aggregates (> 2 mm), macro-aggregates (0.25-2 mm), micro-aggregates (0.053–0.25 mm), and silt-clay (< 0.053 mm) using the wet sieve method. High-throughput sequencing was employed to characterize the bacterial community, and Pearson correlation coefficient was used to reveal the relationship among bacterial community, organic carbon, nitrogen, phosphorus and enzyme activities in soil aggregates. Compared with CK, the results showed that straw returning significantly increased and decreased the contents of > 2 and 0.053–0.25 mm aggregates by 10.64% and 34.15%, respectively. And the content of organic carbon and total nitrogen in aggregate with > 0.053 mm increased by an average of 20.61% and 24.22% respectively in straw returning. Furthermore, straw returning caused significant increases in urease and phosphatase activities of soil aggregates by 121.01% and 29.85%, respectively. Conversely, Chao and Shannon indices of bacterial community of soil aggregates with average decreased values of 2.93% and 0.93%, respectively. Nevertheless, the relative abundances of Chloroflexi, Acidobacteriota, and Nitrospirota increased by 19.07%, 2.58%, and 23.5% in straw amended soil aggregates compared with the conventional fertilization and CK treatments. Our results emphasized on the efficacy of straw returning to improve the soil health/quality through regulating soil structure, increasing the urease and acid phosphatase activities of soil aggregates, enhancing carbon and nitrogen content and change the bacterial structure composition.