Contribution of exudates, arbuscular mycorrhizal fungi and litter depositions to the rhizosphere priming effect induced by grassland species. (January 2015)

• Record Type: Journal Article
• Authors: Shahzad, Tanvir; Chenu, Claire; Genet, Patricia; Barot, Sébastien; Perveen, Nazia; Mougin, Christian; Fontaine, Sébastien
• Is Part Of: Soil biology and biochemistry. Volume 80(2015)
• Page Start: 146
• Page End: 155
• Publication Date: 2015-01
• Subjects: SOM mineralization -- Continuous 13C labeling -- Microbial community -- Priming effect -- Root exudates -- PLFA -- Grasslands; Soil biochemistry -- Periodicals; Soil biology -- Periodicals; Sols -- Biochimie -- Périodiques; Sols -- Biologie -- Périodiques; Sols -- Microbiologie -- Périodiques; Bodembiologie; Biochemie; 631.46
• DOI: 10.1016/j.soilbio.2014.09.023
• Languages: English
• ISSNs: 0038-0717

Abstract

Abstract: The presence of plants induces strong accelerations in soil organic matter (SOM) mineralization by stimulating soil microbial activity – a phenomenon known as the rhizosphere priming effect (RPE). The RPE could be induced by several mechanisms including root exudates, arbuscular mycorrhizal fungi (AMF) and root litter. However the contribution of each of these to rhizosphere priming is unknown due to the complexity involved in studying rhizospheric processes. In order to determine the role of each of these mechanisms, we incubated soils enclosed in nylon meshes that were permeable to exudates, or exudates & AMF or exudates, AMF and roots under three grassland plant species grown on sand. Plants were continuously labeled with 13 C depleted CO2 that allowed distinguishing plant-derived CO2 from soil-derived CO2 . We show that root exudation was the main way by which plants induced RPE (58–96% of total RPE) followed by root litter. AMF did not contribute to rhizosphere priming under the two species that were significantly colonized by them i.e . Poa trivialis and Trifolium repens . Root exudates and root litter differed with respect to their mechanism of inducing RPE. Exudates induced RPE without increasing microbial biomass whereas root litter increased microbial biomass and raised the RPE mediating saprophytic fungi. The RPE efficiency (RPE/unit plant-C assimilated into microbes) was 3–7 times higher for exudates than for root litter. This efficiency of exudates is explained by a microbial allocation of fresh carbon to mineralization activity rather than to growth. These results suggest that root exudation is the main way by which plants stimulated mineralization of soil organic matter. Moreover, the plants through their exudates not only provide energy to soil microorganisms but also seem to control the way the energy is used in order to maximize soil organic matter mineralization and drive their own nutrient supply. Highlights: Role of root exudates, AMF and roots in rhizosphere priming effect (RPE) was disentangled. Differentially permeable meshes and continuous 13 C labeling of grassland monocultures were used. Root exudation induced 58–96 % of total RPE whereas the rest was contributed by roots. RPE efficiency was 3–7 times higher for exudates than roots. Microbial allocation of plant C to mineralizing activity than growth explains higher RPE for exudates.