Response of N turnover, DOC production and soil solution fluxes

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Forest and fen soils are frequently subjected to extended drought periods or to lowering of water table during summer. Many biological and chemical processes in soils are affected by water and oxygen availability, but little is known about the consequences of increasing drought periods on annual matter fluxes for these ecosystems. Here, we quantify and evaluate the effects of changes in precipitation and water table on matter fluxes in soil solution of a forest and a fen at the Fichtelgebirge. Particularly, we will focus on the mechanisms and processes beyond the inorganic N and dissolved organic carbon (DOC) fluxes. The 15N dilution technique and the barometric process separation method will be used to determine the gross N mineralisation and gross nitrification in top soil horizons at different stages of the manipulations. Additionally, in-situ net N mineralisation is scheduled at both sites to estimate the potential availability of inorganic N for plant uptake. The field studies will be accompanied by a laboratory study about the effect of soil water content on N transformation at constant temperature. DOC fluxes and the turnover of soil organic carbon will be simulated using the DyDOC model based on the radiocarbon signature of these fractions.