Abstract
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.
Highlights
In temperate and boreal forests ectomycorrhizas (ECMs) are often symbiotically formed between trees and soil fungi
In this study we found that T. melanosporum ectomycorrhizal colonization significantly increased leaf photosynthetic rate and rhizosphere Total Organic Carbon (TOC) exudates, as well as the rhizosphere pH and acid phosphatase activity
Tuber melanosporum ectomycorrhizal colonization of Q. mongolica shifted rhizosphere bacterial communities towards a community that was enriched with actinobacteria
Summary
In temperate and boreal forests ectomycorrhizas (ECMs) are often symbiotically formed between trees and soil fungi. ECMs can release C and nitrogen (N) exudates including amino acids, organic acids and enzymes to mobilize plant less-available nutrients. In this way ECMs promote soil C and other nutrients cycling, as well as plant nutrients uptake (Smith and Read 2008; Cairney 2011; Wang and Lambers 2020). Root symbiosis with soil mycorrhizal fungi and increased root exudates are two responses to low P availability and both strategies increase plant P acquisition at significant C cost (Lynch et al 2005; Raven et al 2018).
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