Nanoparticles and colloids as vectors of P-losses and -redistribution during forest ecosystem development

Natural nanoparticles and colloids with their large specific surface area and reactivity are primary sorbents of P and thus largely control phosphorus mobility and bioavailability in soils. We plan to continue and expand the fruitful research of phase I of SPP 1685 on the role of natural nanoparticles and colloids in soils, soil leachates and runoff for the phosphorus storage, transfer and losses in forest ecosystems. The different natural nanoparticle and colloid types identified in the first project phase will be further characterised in collaborative column, lysimeter and new field experiments. New aspects in these experiments are the inclusion of a forest ecosystem with a carbonate-containing soil and the exploration stoichiometric linkages between P-, Corg- and N-cycles. To this end, the novel coupling of field-flow-fractionation with ICP-MS and organic carbon detector (OCD) established in the first phase of SPP 1685 for determining concentrations of P and C in combination with Fe, Al, Mn, Ca, Si of nanoparticles, colloids and of the dissolved phase, shall be extended to pioneering the additional detection of organic nitrogen (ON). These extended analytical possibilities will be employed and contribute to the central project of the second phase of SPP 1685. Thereby for the first time, enabling the elucidation of the relevance of colloids for P (re)cycling in forest ecosystems under nutrient limitation and N, P and N+P addition (WP 2.1). Moreover, we will contribute to the joint flux cluster activities by quantifying the lateral and vertical transfer of P bound to nanoparticles and colloids on different spatial scales during peak flow events (WP 2.3). Furthermore, in order to judge the role of these P losses for P recycling, rhizotrone experiments will be conducted with beech seedlings and soil colloids of different P status (WP 2.2). To better characterize the binding of P to nanoparticles and colloids, specific sorption experiments with inorganic and organic P compounds (WP 2.4) and 31P-NMR measurements on natural nanoparticles and colloids will be undertaken. Overall, the outcome of the proposed experiments shall improve our current understanding of P fluxes and cycling not only of forest ecosystems but also of other terrestrial ecosystems.

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