Potassium Fulvate Alleviates Salt–Alkali Stress and Promotes Comprehensive Growth of Oats in Saline–Alkali Soils of the Qaidam Basin

Soil salinization limits global agricultural sustainability, and extensive areas of saline-alkaline soils on the Qinghai-Tibet Plateau remain underutilized. Against this backdrop, this study evaluated the effects and ecological regulatory mechanisms of potassium fulvate (PF) application on oat (<i>Avena sativa</i> L.) growth, soil properties, and rhizosphere microbial communities in the saline-alkali soils of the Qaidam Basin. The results showed that PF significantly enhanced both aboveground and belowground biomass and improved root morphological traits, with the higher application rate (150 kg·hm^-2) showing superior performance. PF also effectively improved soil nutrient conditions (organic matter, ammonium nitrogen, and potassium), reduced the integrated salinity-alkalinity index, significantly optimized the composition of rhizosphere soil cations (increased K⁺ and Ca²⁺; decreased Na⁺ and Mg²⁺), and induced a marked reshaping of the composition and structure of rhizosphere microbial communities. Notably, microbial β-diversity exhibited a significant regulatory effect on the comprehensive growth of oats. Structural equation modeling (SEM) revealed that PF primarily promoted oat growth indirectly by improving soil physicochemical properties (direct effect = 0.94), while the microbial community structure served as a synergistic ecological mediator. This study clarifies the regulatory mechanisms of PF in oat cultivation under alpine saline-alkali conditions, providing both theoretical and practical support for improving soil quality, enhancing forage productivity, and promoting sustainable agriculture in cold regions.