On 16 June at 10:15 Kaarin Parts will defend her doctoral thesis "The impact of climate change on fine roots and root-associated microbial communities in birch and spruce forests".
Senior Research Fellow Ivika Ostonen-Märtin, Institute of Ecology and Earth Sciences, University of Tartu
Professor Emeritus Krista Lõhmus, Institute of Ecology and Earth Sciences, University of Tartu
PhD. Jussi Heinonsalo (Univ. of Helsinki and Finnish Meteorological Institute, Finland)
In the face of rising temperatures and humidity, the functioning and carbon storage of northern European forests is largely dependent on the acclimation ability of fine roots and root-associated microbial communities. We investigated the effects of increased air humidity and soil warming on silver birch (Betula pendula) and spruce (Picea abies and P. sitchensis) fine and absorptive root biomass (FRB, aFRB), absorptive root morphology and the communities of ectomycorrhizal (EcM) fungi and rhizosphere bacteria, comparing results from field manipulation experiments to observations from a small-scale geothermal soil temperature gradient and large-scale latitudinal gradients. We witnessed a uniform morphological response of forming longer and less branched absorptive roots with increased specific root length and area in all studied species to obstructions in nutrient uptake or otherwise stressful growing conditions. Air humidification and a northern location resulted in higher FRB and aFRB, while experimental warming and a southern location caused a decrease in FRB and aFRB and root tissue density, which suggests increased root turnover in warmer soils. Strong trilateral relationships between absorptive root morphology, EcM fungal community and soil bacterial community emerged in the studied birch stands. Humidification caused a shift towards a higher proportion of hydrophilic morphotypes; a higher proportion of long-distance exploration type was recorded in warmer soils. Warming and humidification led to a rise in the proportion of Tomentella spp., possibly related to higher root turnover. On the latitudinal gradient, the soil C:N ratio was the main determinant of variation in absorptive root traits and root-associated microbial community structure. This thesis demonstrates how birches and spruces respond to environmental change through active modifications in root morphology and biomass, concurring with shifts in root-associated microbial community, and all these changes proved to be strongly inter-related. The similar root reactions, irrespective of tree species, stand age, location, or experiment type, permit us to conclude that the observed responses reflect general acclimation patterns, at least for the studied species.