The legacy of rhizosphere: how multi-year root activity fosters soil structure formation and the buildup of soil organic matter

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The aim of the project in the context of the PP 2089 “rhizosphere spatiotemporal organisation” is to investigate the long term (legacy) effects of rhizosphere spatiotemporal development on soil structure and the fate of both root and soil derived organic matter. We will elucidate the intricate connection of plant root activity and organic matter input with the soil structure as modulated by soil texture and root traits. The work will reach from the single root up to the root system, integrating quantitative and qualitative approaches from micrometre to plot scale. We cover single roots in joint lab experiments as well as complete root systems and their long term fate in the field. A major focus will be the elucidation of the persistence of root derived organic matter in distinct rhizosphere soil structures, namely soil micro- and macroaggregates formed due to root activity. These approaches will be based on quantitative and qualitative analyses of the stored C and N pools. At field scale we will determine the long term fate of rhizosphere driven soil structure formation and the persistence of root derived organic matter. We will measure the amounts of C and N and the chemical composition of organic matter in different soil organic matter fractions as well as in distinct soil aggregate size fractions. The persistence of the root derived organic matter in distinct aggregate size classes will be analysed by laboratory scale incubation experiments. We will make use of 13C and 15N isotopic labelling to trace the fate of rhizodeposits into microbial cells and soil compartments in the direct vicinity of the root. The combined approach in collaboration with several other PP participants will allow to provide a fundamental insight into the long term development of root affected soil properties and their persistence over time and will at the same time provide data for modelling soil aggregation in the rhizosphere. With these results we will provide a significant contribution to focal topic iv ‘Carbon sequestration / microaggregate formation / stability of soil structure’ of the PP.