Silicon quantum dots boost soybean productivity and quality through enhanced photosynthesis and nitrogen fixation

Enhancing biological nitrogen fixation (BNF) is a promising strategy to improve crop productivity while reducing dependence on synthetic nitrogen fertilizers. However, existing approaches for enhancing BNF are often constrained by environmental variability and host specificity, whereas the effects of silicon quantum dots (SiQDs) on the coordination of photosynthesis and nitrogen fixation in soybean remain unclear. Here, we investigated the effects of SiQDs on soybean (Glycine max) growth, photosynthesis, nitrogen fixation, and soil-plant interactions. Application of 100 mg kg^-1 SiQDs significantly improved photosynthetic performance, as indicated by increased RuBisCO activity (15.88%) and soluble sugar accumulation (35.79%), and was accompanied by enhanced nodule development, nitrogenase activity (45.93%), and nodule protein content. SiQDs also upregulated key nitrogen transporter genes (AMT and NRT), suggesting enhanced nitrogen uptake and translocation. In parallel, SiQDs altered rhizosphere microbial community structure and predicted functions related to carbon and nitrogen cycling, consistent with increased soil inorganic nitrogen (NH₄⁺-N and NO₃^--N) and organic carbon. These coordinated physiological and rhizosphere responses contributed to improved yield formation, as reflected by a 14.95% increase in 100-grain weight, together with enhanced grain nutritional quality. Random forest analysis further identified soil inorganic nitrogen as a key predictor of yield improvement. Overall, SiQDs enhanced soybean productivity by promoting the coordination between photosynthesis and nitrogen fixation, highlighting their potential as a nano-enabled strategy for improving nitrogen use efficiency in soybean production.