Mountains are particularly affected by climate change: they are warming faster than the lowlands. As the temperature rises, the snow cover is reduced and dwarf shrubs are spreading to higher altitudes - with a strong impact on the seasonal processes of sensitive Alpine ecosystems. This is shown by a new study involving Innsbruck ecologist Michael Bahn, who has carried out field studies over several years in the rear Ötztal valley in Tyrol.
The combination of reduced snow cover and the spread of dwarf shrubs - such as heather (Calluna vulgaris) - disrupts the temporal interaction between plants and soil microorganisms, which is essential for the cycling of nutrients in ecosystems. This disruption may result in high mountain ecosystems being less able to store the essential nutrients that support plant growth. "There is a winter microbial community and a summer community. Snow serves as an insulating blanket and plays an important role in maintaining the fragile ecological balance in the high alpine region. Earlier snowmelt disrupts the seasonal transition of the microbial communities and how they connect to the plant communities. This affects the nutrient balance and plant productivity and jeopardises the balance of the ecosystem," explains Prof. Michael Bahn, head of the Research Group Functional Ecology at the Department of Ecology at the University of Innsbruck. Numerous test areas at an altitude of 2500 metres above Vent in Ötztal provided data for a comprehensive international study, which has now been published in the journal Global Change Biology. Bahn worked on this research together with colleagues from the University of Manchester under the lead of Richard Bardgett alongside experts from the Helmholtz Centre Munich.
Cycles out of balance
Every year, mountain ecosystems experience strong seasonal shifts of nutrients between plants and the microbial communities in alpine soils. After the snow melts in spring, plants start to grow and compete with soil microbes for nutrients, triggering a shift in nutrient storage from the soil to the plants. This process is reversed in autumn when plants die and nutrients are returned to the soil through dead leaves and roots. In winter, snow acts like an insulating blanket: the soil microbes remain active and store the nutrients in their biomass that the plants need when they sprout in the coming spring. Appropriate timing of these processes over the course of the year is therefore essential for this interaction - and this is now in danger of becoming unbalanced: "Climate change is expected to cause a loss of snow cover of up to 80 to 90 per cent in parts of the European Alps by the end of the century and cause the timing of snowmelt to be pushed forward by 5 to 10 weeks," emphasise study authors Bahn and Bardgett. "Our work illustrates how the combination of different impacts of climate change can severely disrupt important ecosystem functions in alpine ecosystems, with potentially long-term consequences for nutrient cycling and biodiversity."
How ecosystems respond to the interplay of multiple simultaneous drivers of global change is still a major challenge for researchers due to the complexity of the systems. As this new study shows, interactions between direct and indirect climate change factors, such as changes in snow cover and the spread of dwarf shrubs, can lead to sudden and unexpected changes in fundamental ecosystem processes.
Publication: Broadbent, A., Newbold, L., Pritchard, W., Michas, A., Goodall, T., Cordero, I., Giunta, A., Snell, H., Pepper, V., Grant, H., Soto, D., Kaufmann, R., Schloter, M., Griffiths, R., Bahn, M., & Bardgett, R. (2024). Climate change disrupts the seasonal coupling of plant and soil microbial nutrient cycling in an alpine ecosystem. Global Change Biology, 30, e17245. https://doi.org/10.1111/gcb.17245
Michael Bahn on the PEAK-Expert-List: https://www.uibk.ac.at/en/peak/expertinnen/michael-bahn/
