Molecular physiology of tree nutrition in mixed and pure beech-conifer forests: interaction with mycorrhizae

PhD Student

Michela Audisio

Research Outline

Ectomycorrhizal (ECM) fungi play important roles in biogeochemical cycles (Finlay 2008) because they mediate nutrient exchange between host plant and soil.
However, several environmental stresses, such as drought or defoliation by pests, may alter photosynthesis and consequently limit carbon supply (Clausing et al. 2020). Under these conditions, nitrogen (N) translocation by ECM fungi can even be withheld (Näsholm et al. 2013). A frequently discussed solution to improve forest resilience and or resistance is the establishment of mixed stands, usually combining native with non-native tree species (Schmiedinger et al. 2009).
Very little is known about the functional diversity of ECM fungi in combination of native with non-native tree species and these fungal communities impact tree nutrition and performance under environmental stresses. In addition, the impact of tree species identity on water availability, which in turn may influence photosynthesis, may have feed-back effects on ECM fungal assemblages and functioning.
Therefore, the final goal of this work is to better understand the links between the composition and functions of fungal assemblages, in particular ECM fungi, forest stand types, and tree nutrition under drought stress, with implications for forest management across Germany in a scenario of changing climate.

Main objectives:

  1. Study N uptake of European beech, Norway spruce and Douglas-fir in homospecific and heterospecific interactions under drought using isotopic tracers. The hypotheses are that the 3 tree species differ in their N uptake strategies, in particular Douglas-fir shows the most significant difference; moreover, we expect that, when facing water shortage, the physiological performance of beech is negatively impacted, and the interactions with conspecifics are more negative than with Douglas-fir.

  2. Identify the response of ECM fungi to drought at the host-tree and forest level. The first hypothesis is that the mycorrhizal status changes accordingly to the specific tree physiological performance under drought. Secondly, the reduction of soil moisture has a negative effect on fungal communities; in beech/Douglas fir mixed forests this effect is less pronounced than in pure conifer forests.

Principal Investigator / Supervisor

Prof. Dr. Andrea Polle, Forest Botany and Tree Physiology, Faculty of Forest Sciences and Forest Ecology