Trichoderma -induced increase in rhizosphere soil bacterial diversity contributed to wolfberry growth promotion in saline land

Abstract

Trichoderma has proved to enhance plant growth under saline stress. However, there is limited research on Trichoderma-induced alterations of rhizosphere microbial communities in woody plants, and the subsequent effect on their yield is poorly understood. This study was to investigate the growth-promoting mechanism of Trichoderma asperellum on wolfberry (Lycium chinense) in coastal saline land from bacterial community and diversity aspects through a field trial with Trichoderma agent application. Trichoderma agent application significantly increased fruit yield, plant dry weight and nitrogen accumulation, demonstrating that Trichoderma enhanced salt tolerance of wolfberry. Despite no obvious influence on the structure of bacterial community, Trichoderma agent application significantly increased rhizosphere soil bacterial diversity, with beneficial bacterial genera including Shinella and Flaviaesturariibacter showing increased relative abundances. In addition, Trichoderma agent application enhanced the stability of soil bacterial co-occurrence network, as evidenced by higher counts of nodes and edges in the network. Furthermore, Trichoderma agent application reduced the abundance of the complete nitrifier Candidatus Nitrospira nitrificans, inhibited soil nitrification and significantly increased soil ammonium nitrogen content, contributing to the improvement of plant nitrogen nutrition. According to random forest analysis, the most significant predictive importance for wolfberry yield was Shannon index, followed by the relative abundances of beneficial bacteria and soil nitrate nitrogen content, highlighting that the growth-promoting role of Trichoderma could be realized by elevating rhizosphere soil bacterial diversity. Moreover, SEM indicates that in contrast to the pathway of nitrogen accumulation, the increased yield was primarily achieved by enhancing rhizosphere soil bacterial diversity with Trichoderma agent application. Therefore, Trichoderma promotes wolfberry growth and yield in saline land mainly by elevating rhizosphere bacterial diversity, with improved nitrogen nutrition providing an additional contribution. This study deepens our understanding of the mechanisms by which Trichoderma promotes plant growth, and provides a promising biostimulant for wolfberry cultivation in saline land.