Research without DFG-funding until 2020
(Karlsruhe Institute of Technology)
Prof. Dr. Martin Kaupenjohann
Element fluxes will respond much more rapidly to changing environmental conditions (including changes in land use and reduced biodiversity) than the soil solid phase or a forest stand itself. Therefore, investigation of element fluxes is a convenient tool to elucidate effects of land use intensity and biodiversity on functioning of both forest and grassland ecosystems of the Biodiversity Exploratories. While it is already known that different land use types, such as forest or grassland, have strong impact on element cycles, consequences of differing management intensities on the same type of land use and associated biodiversity for element cycling in established real world ecosystems are still largely unknown.
Element and nutrient budgets of ecosystems include input (atmospheric deposition, manuring), internal cycling (mineralization, weathering, uptake into biomass, accumulation, translocation) as well as output (leaching, gaseous emission, harvest). The majority of turnover and mass transport takes place in precipitation and soil solution in dissolved form. For both, distribution and retention of elements and nutrients, processes in soil and canopy are important and therefore attract special interest. Many of these processes are mediated biologically and it is therefore assumed that synergies evolve from higher biodiversity levels, which enhance element recycling and decrease nutrient losses.
As a contribution to the elucidation of control variables of stable ecosystem functions and resulting ecosystem services, we examine water flows and nutrient cycling processes of different forest and grassland management systems varying in biodiversity in each of the three exploratories (altogether 56 plots).
1. Nutrient inputs and outflows of ecosystems as well as element cycles are linked to land use intensity and biodiversity.
2. Nutrient and carbon leaching losses are inversely proportional to land use intensity and biodiversity.
3. Turnover and recycling of carbon compounds in ecosystems lead to an approximation of the quality of dissolved organic matter of different ecosystems along water flow paths from the canopy into the subsoil.
For these purposes, we installed rainfall, throughfall and stemflow samplers as well as litter fall collectors to determine atmospheric inputs and turnover processes in the canopy. Element cycling in soils as well as leaching losses are assessed with lysimeters under organic layers of forest floors and suction cups.
In recovered aqueous solutions, we determine concentrations of different C (DIC, DOC, POC), N (DN, PN, NH4-N, NO3-N) and P species (TP, PO4-P), as well as of different elements like S, Na, K, Ca, Mg, Al, Mn and Si. Characterization and determination of the quality of dissolved organic matter (DOM) is carried out using FT-ICR-MS, fluorescence measurements and titration microcalorimetry, while turnover of nutrient elements and their sources are investigated by means of stable isotope approaches (15N). Investigations of 15N signals on deciduous and coniferous tree leaves using nanoscale secondary ion mass spectrometry (NanoSIMS) will provide information on the formation and spatial distribution of particulate N compounds and other nutrients within the microbially colonized phyllosphere of tree leaves. In addition, the composition of the phyllosphere microbial community will be studied in collaboration with the Chair of Aquatic Geomicrobiology (FSU Jena) using molecular techniques.
The results of our research are prerequisites to disentangle effects of land use and biodiversity and to evaluate effects on element cycling
Martin Schwarz, forest