[Effects of Distillery Sewage Sludge on Rhizosphere Soil Quality and Carbon Cycle Functional Genes in Sorghum]

Distillery sewage sludge （DSS）， a typical organic byproduct generated during the production of Chinese Baijiu， has attracted increasing attention for its potential in agricultural resource utilization. However， the ecological effects of different DSS application methods on rhizosphere soil remain unclear. Using brewing sorghum rhizosphere soil as the research object， four application modes （unfertilized control， CK； spherical basal application， BF； spherical lateral application， LF； and powdered mixed application， MF） were comparatively evaluated for their impacts on soil nutrients， enzyme activities， carbon-functional microbial communities， and carbon-cycling functional gene expression. The results showed that， compared with CK， all three DSS treatments （BF， LF， and MF） significantly increased the contents of soil organic matter （SOM）， available nitrogen （AN）， ammonium nitrogen （NH₄⁺-N）， and nitrate nitrogen （NO₃^--N）， with MF achieving the most pronounced effect， raising SOM by 114% （P<0.001）. Meanwhile， DSS application also enhanced soil enzyme activities to varying degrees， with urease （URE） and catalase （CAT） activities increasing by 41.55%-174.47% and 2.83%-30.41%， respectively. Metagenomic analysis revealed that DSS application altered the composition and diversity of carbon-functional microbial communities and elevated the overall expression levels of genes related to carbon degradation， carbon fixation， and methane metabolism. Specifically， MF significantly enhanced the abundance of key genes such as bglX involved in cellulose degradation and those in carbon fixation and degradation pathways， whereas LF promoted the expression of coxL involved in CO oxidation and methane oxidation pathways. Further analysis using a random forest model indicated that soil nitrogen levels and exchangeable Ca and Mg ions under DSS application significantly influenced the expression of carbon cycling functional genes. In conclusion， different DSS application methods regulate the soil nutrient environment and microbial community structure， thereby enhancing the expression of carbon cycling functional genes. Among them， MF was identified as the most effective strategy for improving soil quality and microbial carbon metabolism potential. This study provides theoretical support and mechanistic insight for the efficient utilization of distillery byproducts in circular agriculture and the enhancement of soil ecological functions.