Mycorrhization of Quercus Mongolica Seedlings by Tuber Melanosporum Alters Root Carbon Exudation and Rhizosphere Bacterial Communities

To study how ectomycorrhizas (ECMs) mediate plant performance and rhizosphere soil bacterial communities via altered physiological characteristics and root carbon exudation. Tuber melanosporum-colonized and uncolonized Quercus mongolica seedlings were grown on a substrate consisting of 41% peat, 41% pumice, 9% pine bark and 9% lime. Gas exchange fluorescence system, inductively coupled plasma atomic-emission spectrometer, high-performance liquid chromatography, gas chromatography and mass spectrometry, and 16S rRNA sequencing were used to analyze photosynthetic and nutritional characteristics, rhizosphere carbon exudates, and bacterial communities. Tuber melanosporum mycorrhization increased leaf photosynthetic rate (69%), phosphorus concentration (94%), rhizosphere pH (0.4 units), rhizosphere acid phosphatase activity (33%) and total organic carbon (76%) in rhizosphere extracts but decreased leaf potassium concentration (26%) and rhizosphere organic anions (50%). Additionally, sugars including galactose were present in rhizosphere extract of colonized, but not uncolonized seedlings. Mycorrhization altered rhizosphere bacterial communities, with only ~ 10% operational taxonomic units (OTUs) shared between colonized and uncolonized seedlings; T. melanosporum colonized plants were enriched in actinobacteria. The differential abundances of other bacterial OTUs affected by T. melanosporum colonization were also correlated with variation in plant physiological and/or rhizosphere factors. Our results suggest that T. melanosporum ECM colonization may regulate carbon economy and rhizosphere bacterial communities of Q. mongolica seedlings grown in a previously sterilized peat-based substrate, to promote plant growth and nutrient cycling.