Effects of straw return combined with different amendments on soil enzyme activities and bacterial community...

Soil microorganisms are fundamental drivers of nutrient cycling and ecosystem functioning in agricultural soils, but their responses to management practices in acidic agroecosystems remain insufficiently understood. Acidification-induced changes in soil environmental conditions can constrain bacterial activity and disrupt carbon and nutrient transformation processes. This study investigated how straw return combined with different amendments affects soil enzyme activities and bacterial community structure in acidic purple soil under a 2-year rice-rapeseed rotation system. Six management treatments, including control (CK), conventional fertilization (F), straw return (FT), and straw return combined with calcium-magnesium phosphate fertilizer (FGT), limestone powder (FST), or biochar (FBT), were established to evaluate their effects on soil properties, enzyme activities, and bacterial communities. The results showed that amendment treatments were associated with contrasting changes in soil biochemical properties and bacterial community characteristics. FST treatment effectively alleviated soil acidity and enhanced urease (S-UE) and peroxidase (S-POD) activities, whereas FBT treatment promoted soil organic carbon (SOC) accumulation and stimulated carbon-related enzyme activities. Amendment treatments were associated with variation in bacterial community composition, with treatment-specific differences in dominant bacterial taxa and their associations with soil environmental conditions. Soil pH, SOC, and enzyme activities were important environmental factors associated with bacterial community differentiation. These findings demonstrate that straw return combined with amendments regulates nutrient cycling through amendment-specific bacterial pathways, highlighting the importance of bacterial processes in restoring the health of acidic purple soils and improving the sustainability of their agricultural ecosystems in the Sichuan Basin.