Plant Nutrient Resource Use Strategies Shape Active Rhizosphere Microbiota Through Root Exudation.

Julien P Guyonnet,Mohamed Barakat,Thierry Heulin,Audrey Dubost,Laurent Simon,Martin Guillemet,Feth El Zahar Haichar,Wafa Achouak,Philippe Ortet

doi:10.3389/fpls.2018.01662

Abstract

Plant strategies for soil nutrient uptake have the potential to strongly influence plant–microbiota interactions, due to the competition between plants and microorganisms for soil nutrient acquisition and/or conservation. In the present study, we investigate whether these plant strategies could influence rhizosphere microbial activities via root exudation, and contribute to the microbiota diversification of active bacterial communities colonizing the root-adhering soil (RAS) and inhabiting the root tissues. We applied a DNA-based stable isotope probing (DNA-SIP) approach to six grass species distributed along a gradient of plant nutrient resource strategies, from conservative species, characterized by low nitrogen (N) uptake, a long lifespans and low root exudation level, to exploitative species, characterized by high rates of photosynthesis, rapid rates of N uptake and high root exudation level. We analyzed their (i) associated microbiota composition involved in root exudate assimilation and soil organic matter (SOM) degradation by 16S-rRNA-based metabarcoding. (ii) We determine the impact of root exudation level on microbial activities (denitrification and respiration) by gas chromatography. Measurement of microbial activities revealed an increase in denitrification and respiration activities for microbial communities colonizing the RAS of exploitative species. This increase of microbial activities results probably from a higher exudation rate and more diverse metabolites by exploitative plant species. Furthermore, our results demonstrate that plant nutrient resource strategies have a role in shaping active microbiota. We present evidence demonstrating that plant nutrient use strategies shape active microbiota involved in root exudate assimilation and SOM degradation via root exudation.

Highlights

Several studies have shown that plants can host up to 1000 distinct microbial species in their different organs (Bulgarelli et al, 2013; Hacquard et al, 2015)
In order to determine the impact of root exudation levels of each plant species, measured in our previous work by Guyonnet et al (2018), on microbial activities, respiratory activities are plotted against root exudation level (Figure 1)
The Substrate-induced respiration (SIR) and denitrifying enzymatic assay (DEA) activities in the root-adhering soil (RAS) fraction of the four exploitative species (TF, AO, Bromus erectus (BE), Dactylis glomerata (DG)) were significantly higher than the RAS fractions of the two conservative species (FP, Sesleria caerulea (SC)), which did not differ from the bulk soil (BS)

Summary

Introduction

Several studies have shown that plants can host up to 1000 distinct microbial species in their different organs (Bulgarelli et al, 2013; Hacquard et al, 2015). Plants with lower nutrient uptake and lower photosynthetic activities but higher levels of leaf and root dry mass are referred to as conservative (or slow-growing) plant species (Tilman, 1990; Ryser and Lambers, 1995; Aerts and Chapin, 1999). These contrasted strategies of nutrient management influence the input and output of C-resources, from the assimilation of carbon by photosynthesis to its release in the rhizosphere soil via root exudation (Guyonnet et al, 2018)

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Conclusion