Plant hosts control microbial denitrification activity.

Wafa Achouak,Laurent Simon,Thierry Heulin,Danis Abrouk,Feth el Zahar Haichar,Catherine Lerondelle,Mohamed Barakat,Philippe Ortet,Julien Guyonnet

doi:10.1093/femsec/fiz021

Abstract

In the rhizosphere, complex and dynamic interactions occur between plants and microbial networks that are primarily mediated by root exudation. Plants exude various metabolites that may influence the rhizosphere microbiota. However, few studies have sought to understand the role of root exudation in shaping the functional capacities of the microbiota. In this study, we aimed to determine the impact of plants on the diversity of active microbiota and their ability to denitrify via root exudates. For that purpose, we grew four plant species, Triticum aestivum, Brassica napus, Medicago truncatula and Arabidopsis thaliana separately in the same soil. We extracted RNA from the root-adhering soil and the root tissues, and we analysed the bacterial diversity by using 16S rRNA metabarcoding. We measured denitrification activity and denitrification gene expression (nirK and nirS) from each root-adhering soil sample and the root tissues using gas chromatography and quantitative PCR, respectively. We demonstrated that plant species shape denitrification activity and modulate the diversity of the active microbiota through root exudation. We observed a positive effect of T. aestivum and A. thaliana on denitrification activity and nirK gene expression on the root systems. Together, our results underscore the potential power of host plants in controlling microbial activities.

Highlights

The ability to secrete a wide range of compounds into the rhizosphere is one of the most remarkable metabolic features of plant roots with approximately 5 to 21% of the total photosynthetically fixed carbon being transferred into the rhizosphere through root exudates (Whipps, 1990; Marschner, 1995; Nguyen, 2003)
To investigate the impact of the root exudates produced by each plant species on denitrifying activity, we measured the emission of N2O after nitrate amendment only on each plant root system, without adding any carbon source (Fig. 1A)
A positive effect of the root exudates on denitrification activity was observed on the root system of A. thaliana and T. aestivum, while B. napus appears to alter denitrification activity on the root system through root exudates

Summary

Introduction

The ability to secrete a wide range of compounds into the rhizosphere is one of the most remarkable metabolic features of plant roots with approximately 5 to 21% of the total photosynthetically fixed carbon being transferred into the rhizosphere through root exudates (Whipps, 1990; Marschner, 1995; Nguyen, 2003) These compounds are metabolized by soil-borne microorganisms as carbon and energy sources providing the basis for the establishment of plant-microorganism interactions that benefit plant growth by increasing the availability of mineral nutrients, production of phytohormones, degradation of phytotoxic compounds and suppression of soilborne pathogens (Bais et al, 2006; Philippot et al, 2013; Haichar et al, 2014). Co-occurrences of denitrification genes do not appear to be randomly distributed among taxonomic groups (Graf et al, 2014)

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Conclusion