Rhizodeposition: Processes and Functions in Agroecosystems

The rhizosphere is certainly the most relevant soil hotspot defining the quality and quantity of our crops. Most of the biogeochemical and physical differences between the rhizosphere and the surrounding soil are caused by the release of rhizodeposits into the soil. Rhizodeposits modify the activity and growth rates of heterotrophic soil microorganisms and alter community structure in the vicinity of roots. This impacts 1) soil organic matter decomposition (rhizosphere priming effect) and 2) the C transfer through the decomposer system.

The first part of the presentation focuses on the effect of rhizodeposition on soil organic matter (SOM) turnover. Root morphology (e.g. root hairs) alters exudation and, hence, microbial-mediated processes in the soil. While barley with root hairs enhanced SOM decomposition (69% above unplanted soil), barley without root hairs in comparison suppressed SOM decomposition by 28%. The present study suggests that rhizosphere priming effects are intimately linked to root morphology.

The second part of the presentation concentrates on root-C transfer through the food web of an arable soil. The complexity of soil food webs and the cryptic habitat hamper the analyses of pools, fluxes and turnover rates of C in organisms and the insight into their interactions. Our study showed that, although the fungal C stock was less than half that of bacteria, C transfer from fungi into higher trophic levels by far exceed that from bacterial C. This challenges previous views on the dominance of bacteria in root C dynamics and suggests saprotrophic fungi to function as major agents channelling recent photoassimilates into the soil food web.

*** invited by the BayCEER Steering Committee

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