ZnO Nanofertilizer Reduced Organic Phosphorus Transformation and Altered Microbial Function in Soil for Sustainable Agriculture

The impacts of zinc oxide nanoparticles (ZnO NPs) as nanofertilizers on the transformation of phytogenic organic phosphorus (OP), specifically phytic acid (PA) and soy lecithin (LE), as well as their effects on soil microbial functions, remain insufficiently characterized. This study employed a 60-day soil microuniverse experiment to investigate microbial responses to OP under ZnO NPs exposure, focusing on soil physicochemical properties, phosphorus (P) and Zn species transformations, bacterial community and function. At low concentrations (5 and 20 mg/kg), ZnO NPs did not significantly reduce the available P content, but they reduced the transformation of OP into other P species. Synchrotron-based X-ray absorption near-edge spectroscopy revealed that ZnO NPs increased the relative abundance of PA from 0.6 to 3.5% and LE from 58.4 to 67.1%. Bacterial community composition was influenced by P species rather than ZnO NPs concentration. A coupled biogeochemical cycle among carbon, nitrogen and P was observed, with higher total phosphorus further enhancing the abundance of genes involved in P-related processes, such as OP mineralization genes, which increased 6-, 4-, and 2-fold in PAZ5, LEZ5, and PiZ5, respectively, compared to Z5. Carbon fixation genes generally increased in the P-added groups, exemplified by atoB, which encodes acetoacetyl-CoA thiolase, showing a 3.70-, 3.05-, and 3.47-fold increase compared to Z5. In contrast, denitrification genes, nirS, decreased by 0.08-, 0.10-, and 0.33-fold. These findings shed light on the fate of ZnO nanofertilizers and P, supporting the sustainable application of nanofertilizers and the improvement of soil fertility.