P08 Mycorrhizal functions in the forest floor

The mycorrhizal symbiosis is a central component of plant-soil feedbacks and carbon (C) cycles of forest ecosystems. Yet even though it is known that the two major mycorrhizal association types influence litter decomposition and soil organic matter formation differently, it remains unresolved whether this also influences their preference for the forest floor (FF) as a habitat. We hypothesize that mycorrhizal fungi are more dependent on FF C in cold or warm nutrient-poor forest stands, since less photosynthates are produced and invested into the fungal symbiont. As a result, the diversity of the mycorrhizal fungal community in the FF increases.

The aim of my doctoral project is to analyse the response of the mycorrhizal fungal community structure and its functions in the forest floor and mineral soil of temperate mixed beech forests to gradients of temperature and phosphorus availability. I combine functional root trait analyses, an isotopic fractionation analysis, a ¹³C- and ¹⁵N-labeling experiment, and extracellular enzyme analyses with next generation sequencing of the mycorrhizal fungal community in the FF and mineral soil of nine silicate forests composed of European beech (Fagus sylvatica L.; ectomycorrhizal host) admixed with sycamore maple (Acer pseudoplatanus L.; arbuscular mycorrhizal host). My measurements will assess the fungal habitat in roots, the C investment by trees into their mycorrhizal symbionts and the consequences for litter decomposition across the investigated gradients. In addition, I investigate the influence of the microbial and mycorrhizal fungal community composition on root exudation in close cooperation with P7 and P9. My project will refine our understanding and prediction of the ecology of mycorrhizal fungi in the FF of mixed beech forests, which are increasingly exposed to rising temperature and P limitation.