Relevance of root growth and related soil structure formation for spatiotemporal patterns of chemical and biological properties and emergent system functions

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A prerequisite for identification of patterns in the rhizosphere is the localization of roots in situ as they grow. Roots, being sinks and/or sources of radial transport processes, are the starting point for pattern formation. At the same time they constantly alter boundary conditions for transport through soil structure modifcations in their immediate vicinity.In phase 1 we addressed root system architecture (RSA) over time and the extent to which the absence of elongated hairs leads to compensatory mechanisms at the root segment or root system scale and whether differences in pattern formation (physical and chemical) occur as a function of soil substrate (sand vs. loam). We related observed changes at the plant system scale to nutrient uptake, biomass production and soil infiltration as emerging properties.Substrate showed a surprisingly large effect on root traits in general (P1) and on root diameter and root decomposition in particular. Therefore in phase 2, we will focus on deciphering the mechanisms underlying these changes in root diameter and decomposition and their consequences for pattern formation such as chemical gradients, biopore recycling and carbon flux. The root phene ‘increased root diameter’ can be induced by ethylene. Changes in ethylene concentration may result from changes in ethylene production and/or changes in ethylene diffusion in the rhizosphere. In a series of lab experiments we will test, whether such changes do occur and whether they can be related to soil mechanical properties or root-soil contact. The latter is supposed to differ systematically between the two substrates. Differences in root degradation may also be related to ethylene as altered geometry as well as altered chemical composition will affect decay and hence carbon flux.In these lab experiments we will measure ethylene concentration in the soil gas phase and the root-soil contact area for roots of different diameter classes as well as root decay. We will also investigate root diameters in biopores and how radial chemical gradients are affected. The experiments will be conducted in cooperation with other partners for simultaneous analyses of root genes involved in ethylene synthesis and signalling (P7, P8), and soil microbiota altering rhizosphere ethylene concentrations (P14, P17). Soil mechanical impedance (P23) will be characterised and root exudation (P11) will be measured. Ethylene diffusion in the system will be modelled by P4 based on measured soil structure. For root decay and carbon flux we cooperate with P19.The soil plot experiment will be harnessed to investigate long-term changes in soil structure like the build-up of biopore density and its consequences for infiltration capacity and water retention as an emergent property at the field scale.