Project Details
Projekt
Hot gradients & cold spots - spatial relation of carbon dispersal and microbial nutrient immobilization in the rhizosphere and consequences for plant nutrition
Applicants
Dr. Martina Gocke; Professorin Dr. Eva Lehndorff
Subject Area
Soil Sciences
Ecology and Biodiversity of Plants and Ecosystems
Ecology and Biodiversity of Plants and Ecosystems
Term
since 2018
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 403670844
Carbon (C) dispersal, organic matter transformation and nutrient immobilization likely have specific spatial arrangement in the root-soil system. In a basic understanding of rhizosphere dynamics, spatial distribution starts with root exudation at the plant root and leads to gradual changes in rhizosphere chemistry and biology. In Phase 1 we hypothesized that the morphology of roots and properties of soil, especially its texture, control gradual dispersal of C. We found means to analyze C dispersion on the micrometer-scale and observed considerable differences which were predominantly controlled by root morphology. We further hypothesized that transformation of C is done by microbes forming organic substances such as polysaccharides, phospholipid fatty acids and fatty acids and were able to follow this on the millimeter scale. These findings give rise to following new hypotheses that i) a consequence of C dispersal by root exudation is the immobilization of organically bound nutrients in sites with low turnover, so-called cold spots, and that these sites occur in specific regions in the rhizosphere, ii) in soil with low root biomass degradation (as observed for sandy soil in phase 1) immobilization of nutrients in the rhizosphere increases and competes with plant nutrition, and iii) under drought nutrient mobilization processes shift from soil solution to fungal networks. We will continue to use 2D micrometer-scale approaches such as laser ablation isotope ratio monitoring for C turnover analyses (LA-IRMS), extend to NanoSIMS for N dispersal analyses, and include SEM-EDX/WDX to trace immobilization of nutrients such as N and P via a spatial stoichiometric approach. Our millimeter-scale sampling approach established in phase 1 for organic substance characterization, we will now use to identify, quantify and allocate immobilized N and P using compound- or fraction-specific d13C and d15N analyses on microbial necromass N and P (amino sugar and organic P analyses). With our emerging hypotheses we have close links to projects P3, P8, P13, P19, P21, P24, and P25. We will establish a new spatial data set on organic matter distribution in rhizospheres helping to understand processes of C dispersal, nutrient immobilization and mobilization under different external and internal controls, such as soil properties, root morphology and drought. This data can then be implemented in simulation and modeling approaches allocated within the SPP 2089, allowing to transfer knowledge also to other soils and plant species.
DFG Programme
Priority Programmes
