Short-term effects of different forms of straw return on rhizosphere and bulk soil bacterial communities and microenvironmental conditions in saline-alkali maize fields

Salt stress and low nutrient availability in saline-alkali soils constrain crop productivity. However, the effects of different forms of exogenous carbon input on rhizosphere bacterial communities and their predicted functional potential remain unclear. A field experiment was conducted in a coastal saline-alkali maize field with four treatments: no organic amendment (CK), crushed straw return (CS), straw biochar return (CB), and granulated straw return (GS). The effects of different straw forms on soil physicochemical properties, bacterial community structure, predicted functional profiles, and maize yield were compared between rhizosphere and bulk soils. Compared with CK, GS significantly reduced rhizosphere electrical conductivity (EC) and salt content by 57.97% and 59.56%, respectively. Among the different straw forms, GS resulted in significantly lower rhizosphere salt content than CS and CB, while its EC was comparable to CS. Both CS and GS significantly increased rhizosphere available phosphorus content and increased maize yield by 24.87% and 23.35%, respectively. Straw-return treatments significantly altered bacterial community structure in both rhizosphere and bulk soils, with GS enriching a greater number of treatment-specific bacterial taxa in both habitats. Functional prediction based on bacterial community composition showed that, compared with CK, GS was associated with significantly lower predicted relative abundances of multiple MetaCyc pathways related to aerobic respiration, the tricarboxylic acid cycle, and branched-chain amino acid biosynthesis in both rhizosphere and bulk soils. Overall, different straw-return forms exerted distinct short-term effects on the soil microenvironment and bacterial communities. Notably, GS showed a relative advantage in reducing rhizosphere salinity, particularly salt content, while both CS and GS improved rhizosphere nutrient conditions and maize yield.