Phosphorus mobilization in acid forest soils as affected by interactions of water regime, fertilization and growth of beech

Part 2 (SNF): P mobilization potential at the micro scale

Little is known how different water regimes affect the mobilization and bioavailability of phosphorus (P) in acidic forest soils. Of particular interest are sequences of dry and wet periods, predicted to increase as a consequence of climate change. In this PhD project P cycling is studied on the two most contrary sites of the SPP program, Bad Brückenau (rich in P, Silty clay loam) and Lüss (P poor, Loamy sand). The objective of the study is to assess the effects of different water regimes on the mobilization of P and its availability to microorganisms and beech trees. Water regimes will be manipulated in fully randomized greenhouse experiments with beech saplings growing in undisturbed topsoil cores. Parallel to a control kept approximately at field capacity, soil cores will be dried to a water potential of -1000 hPa and then re-wetted at different rates to -10 hPa. In collaboration with the research group of Emmanuel Frossard (ETH Zürich), labelling experiments with 33P will be done in order to study the competition between plants and microorganisms. In addition, soil cores will be randomly probed to assess the spatial heterogeneity in phosphatase activity, which is considered an indicator of the potential to mineralize organic P. Ion exchange membranes will be applied in the same manner to sample low-molecular weight carboxylates, indicators of the potential to mobilize inorganically bound P.
 

There is close collaboration with part 1 of this project on P mobilization/immobilization at the soil column scale (DFG).