Mechanisms of Bio-Based Paper Mulch and Calcium Sulfonate Water-Soluble Fertilizer in Ameliorating Saline-Alkali Soils

Background and Aims Soil salinization threatens agricultural productivity and ecosystem health. Bio-based paper film and bio-based calcium sulfonate have the potential to reduce salinity and enhance ecosystem multifunctionality (EMF). However, their mechanisms in heavily saline-alkali soils remain unclear. Methods A pot experiment was conducted with five treatments: CK (water only), M2 (17.00 g·pot ^− 1 bio-based paper film + 25.00 g·pot ^− 1 bio-based calcium sulfonate), M4 (27.20 g·pot ^− 1 bio-based paper film + 25.00 g·pot ^− 1 bio-based calcium sulfonate), M55 (37.40 g·pot ^− 1 bio-based paper film + 25.00 g·pot ^− 1 bio-based calcium sulfonate), and JF (microbial fertilizer + PVC film). Soil properties, microbial communities, and EMF were analyzed. Results M4 showed the best performance. Compared with CK, it promoted alfalfa (Medicago sativa) germination and growth and increased rhizosphere organic acids. It reduced soil pH and electrical conductivity (EC) and increased soil temperature, moisture, nutrients, and enzyme activities. Although microbial alpha diversity decreased, bacterial and fungal community structures were optimized, forming a more cooperative and complex network. Beneficial taxa involved in nitrogen fixation and phosphate solubilization (e.g., Pseudomonadota, Alphaproteobacteria, and Anaerolineae) were enriched. The higher abundance of Basidiomycota enhanced cellulose and lignin decomposition. Conclusions The combined application of bio-based paper film and calcium sulfonate improved soil quality and reshaped microbial communities, thereby enhancing ecosystem functioning in saline-alkali soils.