Mycorrhization of Quercus mongolica seedlings by Tuber melanosporum alters root carbon exudation and rhizosphere bacterial communities

Aims: To study how ectomycorrhizas (ECMs) mediate plant performance and rhizosphere soil bacterial communities via altered physiological characteristics and root carbon exudation. Methods: 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. Results: 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. Conclusion: 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.