Spatio-temporal pattern of root exudation and enzyme activities in the rhizosphere

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Root exudates are the main driver for biochemical spatio-temporal self-organization of the rhizosphere. We hypothesize that the interactions of roots with soil microorganisms is an efficient strategy to overcome nutrient deficiency locally - in the rhizosphere - by joint (roots and microbial) production of complementary and efficient enzyme systems for mobilization of nutrients for plants. The gradients of enzyme distribution in the rhizosphere will be specified at optimal and deficient nutrient supply. The effects of root exudates on kinetic parameters and enzyme efficiencies will be investigated by zymography in the common field experiment (CFE).Effect of root hairs on microbial functions will be explored based on the microbial allocation theory, which we representatively test at the example of nitrogen (N), hypothesizing that N deficiencies stimulate the production of N acquiring enzymes with high substrate affinity. The efficiency of enzymes produced in the rhizosphere with/without root hairs will be determined based on the Km changes and will be compared with the 15N uptake by maize plants from 15N labeled litter. To quantify and localize the enzymes mineralizing N and boron (B) from soil organic matter, kinetics of enzymes involved in C, N and B cycles will be determined in soil under two maize varieties: with and without root hairs. The spatio-temporal pattern of rhizodeposition and enzyme activities will be analyzed by coupling 14C imaging with localization of enzyme activities by zymography, depending on root hair presence and soil texture to create a picture of rhizosphere self-organization around the growing root. Combining the 2D zymography with micro computed tomography to unravel the distribution and connectivity of pores in soil, we will develop the new approach of 3D zymography. This approach will be offered for other projects in the 2nd phase of the SPP.Based on combination of zymography with radioisotope imaging and enzyme kinetics in hotspots around the growing roots, we will draw fundamental conclusions about root-microbial interactions with respect to the localized mobilization of N and B, and consequences for spatio-temporal pattern of rhizosphere self-organization.