Carbon and Nitrogen flow through the Plant-Mycorrhiza-Soil continuum

All plants release a substantial fraction of the carbon they assimilate via photosynthesis as root exudates into the soil, an input that significantly shapes soil microbial processes. Root exudates are known to accelerate microbial decomposition of soil organic matter in the so called ‘rhizosphere priming effect’.

Rhizosphere priming increases both plant nutrient availability and the release of CO2 from soil to the atmosphere, thereby fundamentally influencing the terrestrial carbon cycle. While the carbon transfer from plants to soil via root exudates has been widely studied, only little is known about a possible transfer of recent carbon from plant to soil microbes via mycorrhizal fungal hyphae exudations. Do mycorrhizal fungi accelerate microbial decomposition of soil organic matter in a similar way to plant roots, by something like a ‘hyphosphere priming effect’? Given that almost 90% of all land plants have associations with mycorrhizal fungi this may be an important, but overlooked pathway for soil priming.

To assess the possible role of mycorrhizal fungi for soil C and N turnover it is necessary to understand mechanisms of C and N exchange along the possibly tripartite partnership among plants, mycorrhizal fungi and soil bacteria. We are using stable-isotope approaches (i.e. EA-IRMS, GC-IRMS and GC-MS-based measurements of plant, soil and soil microbial communities) to trace the flow of photosynthesized C and soil-added N through the plant-mycorrhiza-soil continuum of young beech (Fagus sylvatica) trees harboring a diverse set of mycorrhizal fungi. We aim to use nano-scale secondary ion mass spectrometry (NanoSIMS) to visualize 13C and 15N flow directly across the plant-fungus interface in mycorrhizal roots, and – in collaboration with collegues from the Division of Microbial Ecology (DOME, Group of Dagmar Woebken: Marlies Dietrich, Raphael Gabriel) - the fungus-microbe interface on fungal hyphae. Within this collaboration, the project also aims to analyse the microbiome associated with mycorrhizal root tips and hyphae.

Light and electron microscopy work, as well as sample preparations for NanoSIMS analysis are carried out at, and supported by the Core Facility for Cell Imaging and Ultrastructure Research/University of Vienna (CIUS), in collaboration with Marieluise Weidinger, Irene Lichtscheidl, and Siegfried Reipert. NanoSIMS analysis is carried out by Arno Schintlmeister.

 
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Microbes on mycorrhizal root tip © CeMESS

Experimental setup