Surface Charge Dependent Foliar Applied Silicon Quantum Dots Enhance Soybean Salt Tolerance Through Leaf‐Root‐Microbial Responses

ABSTRACT Here, we evaluated foliar‐applied silicon quantum dots (SiQDs) with different surface charges on soybean salt tolerance. Positively charged SiQDs (P‐SiQDs) exhibited stronger foliar retention and penetration than negatively charged SiQDs (N‐SiQDs), resulting in a 35.3% higher silicon accumulation in leaves. Under 200 mM NaCl stress, foliar application of P‐SiQDs increased shoot dry weight and reduced the Na + /K + ratio. Compared with N‐SiQDs, P‐SiQDs more effectively alleviated salt‐induced damage to thylakoid ultrastructure and improved photosynthetic performance. A life cycle field pot trial further showed that SiQDs increased the 100‐seed weight by 20.1%–25.9% under salt stress. Leaf metabolomics showed significant alterations in lipid metabolite pathways associated with redox homeostasis, accompanied by shifts in the phyllosphere microbiome. P‐SiQDs increased the abundance of Chloroflexota, Actinomycetota, and genera such as Paenarthrobacter , Variovorax , and Xanthobacter . Meanwhile, the phyllosphere microbiome shifted toward life‐history strategies related to growth, resource acquisition, and salt stress tolerance. In addition, P‐SiQDs promoted root growth, nodulation, and nitrogenase activity, leghemoglobin content, and total nitrogen accumulation, together with changes in root exudate composition and the enrichment of salt‐tolerant rhizosphere bacteria, including Sphingomonas and Novosphingobium . These findings indicate that surface charge modification is an effective strategy to enhance the efficiency of foliar nano‐fertilizer application.