Humic Acid‐Derived Carbon Dots Promote Soybean Growth via Enhancing Photosynthesis and Symbiotic Nitrogen Fixation

ABSTRACT Carbon dots (CDs), as a class of carbon‐based nanomaterials have been confirmed to have great potential in promoting crop growth, but its molecular mechanism remains largely unknown. In this study, novel soluble humic acid‐ derived CDs (HA‐CDs) was developed and it could promote soybean growth and symbiotic nitrogen fixation (SNF) within a certain concentration range, which significantly lowered than the precursor. Further biochemical and molecular‐level analyses revealed that this growth‐ and SNF‐promoting effects of HA‐CDs was mainly due to improving the photosynthesis, regulating C/N metabolism and antioxidant enzyme activity of host, and enhancing rhizobial growth and its symbiotic ability with soybeans that depended on the genes rsh and rpoZ . This study provided significant advance in our understanding of the molecular mechanism of HA‐CDs on legume growth and nitrogen fixation, as well as the potential application value of HA‐CDs in agriculture system.