Elemental cycling in forests and grasslands of Biodiversity Exploratories: Response to management intensity and biodiversity

1. Nutrient inputs and outputs of ecosystems and element cycling are linked to land use intensity and biodiversity.

2. losses of nutrients and carbon with leachate are inversely proportional to land use intensity and biodiversity of forest and grassland ecosystems.

3. the conversion and recycling of carbon compounds in ecosystems leads to an equalisation of the quality of dissolved organic matter of different ecosystems along the water flow path from the canopy to the subsoil.

For this purpose, outdoor precipitation, stand precipitation and stemflow collectors as well as litterfall collectors were set up to record both atmospheric substance input and conversion processes in the canopy. Conversions in the soil and losses with the seepage water are elucidated with the help of lysimeters under the organic forest soil layers and suction candles.

In the aqueous solutions obtained, we determine concentrations of various C (dissolved inorganic carbon = DIC, dissolved organic carbon = DOC, particulate organic carbon = POC), N (dissolved nitrogen = DN, particulate nitrogen = PN, NH4-N, NO3-N) and P species (total phosphorus = TP, PO4-P), as well as elements such as S, Na, K, Ca, Mg, Al, Mn and Si. The characterisation and determination of the quality of dissolved organic matter (DOM) is carried out by FT-ICR-MS, fluorescence measurements and titration microcalorimetry, turnover of nutrients and their sources are investigated by stable isotope approaches (15N). Investigations of 15N signals on deciduous and coniferous tree leaves using nano-secondary ion mass spectrometry (NanoSIMS) will provide information on the formation and spatial distribution of particulate N compounds and other nutrients in the microbially colonised leaf space of trees. In addition, the composition of the microbial phyllosphere community will be investigated molecularly in cooperation with the Chair of Aquatic Geomicrobiology (FSU Jena).

The results of our investigations are a prerequisite for separating land use and biodiversity effects from each other and evaluating them in terms of their impact on material cycles.