Matter cycling and nutrient efficiency in mixed and pure stands
PhD StudentKlara Mrak
Research OutlineWe aim to evaluate Douglas fir as an admixture to European beech from a soil ecological perspective by predicting changes in soil carbon and nitrogen stocks, nutritional strategies of the species and nutrient cycling in the ecosystem. Douglas fir seems to be an efficient user and recycler of nutrients both at tree as well as stand level. In a managed forest ecosystem, such a species can close nutrient loops, particularly of nitrogen (N), reduce leaching and groundwater degradation, lessen base cation loss (Ca2+, Mg2+), enhance stand productivity and therefore promote C sequestration in future.
The effect of species identity and species mixtures on soil C and N stocks and SOM quality, however, may not be consistent across site conditions (results of SP 3-1). In the second phase we would like to see if tree-specific traits affecting nutrient mobilization and nutrient use efficiency of European beech and Douglas fir will differ on contrasting sites (e.g., sandy versus loamy) and if they will change when grown in pure versus mixed stands. Furthermore, we would like to gather evidence on site-dependent SOM stabilization which was shown in the first phase by taking a closer look at soil respiration.
N fluxes will be investigated by sampling soil solution with suctions lysimeters and monitoring N inputs by using litter traps and throughfall collectors over multiple years (collaboration with SP 3-1) to see how nitrate concentrations change under Douglas fir depending on site and mixture.
Nutritional strategies of Douglas fir and European beech, grown in pure and mixed stands, will be studied in an in-situ experiment using stable isotope tracers (15N).
Soil respiration will be measured using closed gas flux chambers set up on contrasting sites. Data will be evaluated with regard to results of SP 3-1 in this phase and used by the PhD candidate of the next phase as a basis for modelling approaches.