Functional role of mycorrhizae in the competition for nitrogen in beech-dominated forests. - Institute of Forest Botany, University Göttingen.

Beech trees form symbiotic associations with ectomycorrhizal fungi (EMF) in which the fungi supplies the host tree with nutrients and water in exchange for carbohydrates provided by the host. A tree can associate with various EMF species simultaneously and it is hypothesized that the EMF species composition of a tree is adapted to the prevailing environmental conditions.
The aim of this project is to examine the functional role of these EMF communities in nitrogen nutrition in beech forests and their response to environmental change concerning nitrogen and carbon supply. Therefore, it will be tested whether
(1) a shift in EMF communities takes place in response to nitrogen and carbon supply,
(2) the N-uptake of hyphae and roots change in response to nitrogen supply,
(3) different water regimes influence the N-uptake,
(4) different EMF species in a community differ in N-uptake,
(5) the rate of mycorrhization decreases with nitrogen fertilization and whether a competitor reverse this effect.

To examine changes in EMF communities and in the degree of mycorrhization N-fertilization experiments are carried out under glasshouse conditions at the GSF in Munich. N-uptake of hyphae under field conditions are being measured using mesh bags and stable nitrogen isotopes. N-uptake of roots and hyphae is examined in growth boxes with separated roots and hyphal compartments at the Institute of Forest Botany in Göttingen.