Spatiotemporal plasticity of carbon allocation and rhizodeposition in the maize root system and its impact on the rhizosphere microbiome

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Plants transfer a substantial part of recently fixed carbon (RFC) belowground to build up root structure and to provide energy for root functions. Beyond that, plant derived C fuels microbial life in the rhizosphere. However, spatiotemporal relationships between root architecture, RFC allocation and the rhizosphere microbiome are currently little understood. In the first phase of this project we found spatiotemporal allocation patterns of RFC within the root system. RFC accumulated strongest at root tips and in particular at the most recently emerged crown root tips. Microbial community composition in the rhizosphere responded to these patterns, though more strongly to root types. The underlying causes of variation in root C allocation in dependence on root type and its temporal dynamics as drivers for microbiome structure and function need further investigations. In this follow up project, we propose to gain mechanistic understanding between root and rhizosphere processes by introducing soil heterogeneity (i.e. a soil compaction layer) and therewith challenge root plasticity. We hypothesize that local disturbance introduces changes in root growth and allocation of RFC with consequences on the rhizosphere microbiome. We will apply Magnetic Resonance Imaging in combination with Positron Emission Tomography for non-invasive 4D quantification of root traits and RFC allocation. Transfer of RFC into the rhizosphere and its incorporation by microorganisms (bacteria, fungi, protists) will be tracked after 13CO2 labelling by RNA-SIP. For a comprehensive understanding of the dynamic responses, we will complement our approach by root transcriptomics and rhizosphere metatranscriptomics. This will provide a holistic view on the causes and consequences of altered RFC allocation on microbial rhizosphere processes. Our project will thus provide significant knowledge about principles underlying the development of self-organized spatiotemporal patterns in the rhizosphere, which is relevant for a mechanistic understanding of plant performance.