The impact of climate change on ectomycorrhizal community structure and extracellular enzyme acitivities at the alpine treeline

Climate change may strongly influence species distribution and, thus, the structure and function of ecosystems. The trees form ectomycorrhizal (ECM) associations with soil fungi that are central to ecosystem carbon balance as determinants of plant community structure and as decomposers of soil organic matter. This study will measure the response in ECM fungal community structure and functioning, as well as the soil enzyme activities surrounding the host tree, to a five -year soil warming treatment in an experimental site Stillberg at the Swiss alpine treeline (2180 m a.s.l.). It will also assess whether these parameters respond differently when the two different ECM tree species Pinus mugo ssp. uncinata and Larix decidua are taken into account. We hypothesize that (1) soil warming leads to a shift in the ectomycorrhizal community structure, because fungal species acclimatize differently to elevated temperatures and changed nutrient availabilities in the soil, as well as changed rates of carbon allocated by their hosts. (2) Soil warming influences the rates of enzyme activities in the ECM root tips and in the soil, given that elevated temperatures normally enhance the chemical reactions in the soil and assuming that changed nutrient availabilities and microbial species composition will impact extracellular enzyme production. We will assess the ECM community on the root system of host trees by macroscopic characters combined with molecular analyses and in the soil by next generation sequencing technologies. We will quantify the biomass of fine roots, the proportion of root tips infected by ECM fungi as well as the proportion of non-vital root tips. We will measure the potential enzyme activities of seven hydrolytic and one oxidising enzymes involved in the degradation of organic matter directly on ECM root tips and in different soil layers by using fluorimetric and calorimetric microplate assays. Our analysis will combine morphological/molecular ECM identities with simultaneous ECM root tips and soil enzyme activity profiles of different host trees and soil parameters to identify the levels of organization at which soil warming is translated into altered ecosystem function.