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Linking aggregate formation to small-scale P distribution and P availability in soils

Project staff

  • Simon Stahr
  • Prof. Dr. Friederike Lang
  • Dr. Helmer Schack-Kirchner

Project description

The soil architecture, that is the arrangement of the different components of the solid phase, controls the size and shape of P pathways between the binding sites and the biological P acceptors and donators, respectively. The formation of soil aggregates, defined here as clusters of soil particles, might be induced physically (swelling and shrinking) or biologically (with bioturbation and/or biogenic aggregate glues). Till now hardly anything is known about (1) the controls of aggregate formation and properties in forest soils (2) the relevance of aggregate formation for P-distribution within aggregates and (3) consequences for P availability and mobility. Our own preliminary experiments support that the occlusion of P within forest soil aggregates decreases P plant availability in mineral soils with low biological activity.
Our aim is to analyse the interaction between P nutrition strategies, the formation and properties of soil aggregates and the P-distribution within aggregates. We hypothesise, that aggregate turnover, P-diffusion within aggregates and P-input control the distribution of P within aggregates, inducing the enrichment of P at the aggregate surface especially in soils of intermediate P availability.
We will analyse the stability of natural soil aggregates, their size distribution, occluded organic matter and porosity and the distribution and speciation of P within the aggregates of the acid study sites. Aggregates will be provided differently: softly shaking the soil material, by sieving soil samples (< 2mm) in a field moist state as well as after ultrasonic dispersion. Microdialysis will be used to determine the rate of P-diffusion by on-site measurements. Furthermore, we will analyse and model the leaching of dissolved P from structured and ultrasound-dispersed soil columns. Data on microbial characteristics and root growth and turnover will help to identify controls on aggregate stability. Our project will help to identify site conditions where the aggregation is highly relevant for plant availability of P. Ecological controls of soil architecture will be identified and implications for P availability will be deduced.