Rhizospheric melatonin application enhances low temperature tolerance in barley via regulating the nitrogen-cycling related microorganisms

Rhizospheric melatonin application has a positive effect on the tolerance of plants to low temperature; however, it remains unknown whether the rhizosphere microorganisms are involved in this process. The aim of this study was to investigate the effect of exogenous melatonin on the diversity and functioning of fungi and bacteria in rhizosphere and its implications in enhancing low temperature tolerance of barley plant. The results showed that rhizospheric melatonin application enhanced the low temperature tolerance by maintaining a better photosynthetic carbon assimilation and redox homeostasis. These effects were associated with an altered diversity of microbial community in rhizosphere, especially the species and relative abundance of nitrogen cycling related microorganisms, as exemplified by the changes in rhizosphere metabolites in the pathways of amino acid synthesis and metabolism. Collectively, it was suggested that the altered rhizospheric microbial status upon melatonin application contributed to the enhanced low temperature tolerance in barley plant, and this finding provide some novel insights into the roles of microorganisms in the process of melatonin-induced low temperature tolerance in plant.