Surface Charge Dependent Foliar Applied Silicon Quantum Dots Enhance Soybean Salt Tolerance Through...

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.