White-rot fungus Ceriporia lacerata HG2011 improved the biological nitrogen fixation of soybean and the underlying mechanisms

Aims The improvement of biological nitrogen fixation (BNF) is beneficial to improving legume yield and soil fertility. Thus, the potential of a white-rot fungus Ceriporia lacerata HG2011 in promoting soybean BNF and yield along with the mechanisms was investigated. Methods Fungal metabolites and the effects of C. lacerata HG2011 on rhizobial growth, chemotaxis, and biofilm formation were investigated through pure culture. Soybeans inoculated with this fungus were grown in the climatic cabinet, greenhouse, and field for measuring nodulation parameters, BNF-related enzyme activity, BNF, and yield. Results Although C. lacerata HG2011 had no significant influence on the growth of the rhizobium Ensifer fredii S2-1, the rhizobial chemotaxis and biofilm formation were improved by this fungus broth in pure culture. C. lacerata HG2011 dwelled on the root surface, increased root tips and surface area, produced the nodulation-associated metabolites (phytohormones, flavonoids, and low-molecular-weight organic acids) and hydrolases (cellulase, pectinase, protease, and phosphatase), mobilized soil P and Fe, and stimulated the activities of plant BNF-related enzymes (nitrogenase, glutamine synthetase, and dehydrogenase). Compared with fungus-free control plants, C. lacerata HG2011 improved nodulation and increased %Ndfa by 3.61–4.64%, BNF by 29.26–40.68%, nutrients uptake (N, P, and K) by 4.38–19.60%, and mean grain yield by 10.55% in the fields. Conclusion C. lacerata HG2011 promoted rhizobial chemotaxis as well as soybean nodulation and BNF via releasing phytohormones and improving mineral nutrition. Thus, the fungal inoculant significantly increased soybean yield in both greenhouse and fields, showing a promising application in legume cultivation.