The microecological mechanism of Cordyceps chanhua promoting soil nitrogen cycling

The nitrogen cycle is crucial to the function of the Earth's biosphere. Entomogenous fungi have been proven to promote nitrogen metabolism and cycling in host insects, and transfer nitrogen from insects to soil. However, little is known about the microecological mechanism of entomogenous fungus participating in nitrogen cycling and the microecological impact of exonitrogen from entomogenous fungus on soil.

Here, we report that the entomogenous fungus Cordyceps chanhua secretes nitrate nitrogen and organic nitrogen from its mycelia into the soil environment and absorbs ammonium nitrogen, nitrite nitrogen and hydroxylamine nitrogen from the soil environment into the C. chanhua. Along with the nitrogen exchange process, the bacterial communities related to nitrogen metabolism in the sclerotium of C. chanhua emerge in the soil environment, promoting the soil organic nitrogen cycling process. Redundancy analysis demonstrated that the endogenous/symbiotic bacterial communities within C. chanhua have the greatest impact on ammonium nitrogen and organic nitrogen at the genus level. During the growth process of C. chanhua, the diversity of the bacterial community in its microenvironment significantly decreased. Consistent with this, this study also verified that the exonitrogen of C. chanhua can reduce the diversity of bacterial communities in the soil environment and enrich the bacterial group of Sporosarcina spp., which has a positive promoting effect on nitrogen metabolism. Furthermore, we isolated three highly active nitrogen-transforming dominant strains from the sclerotia of C. chanhua, which further indicates that the nitrogen transport of C. chanhua is closely related to the bacterial community in its mycelia.

The results of this study demonstrate that the associated/endophytic bacteria of C. chanhua facilitates the participation of C. chanhua in soil nitrogen cycling in its microenvironment.