Cross-season legacy effects of climate extremes on alpine soil microbial communities: resilience, regimes shifts and biogeochemical cycles

Soil contains a vast diversity of microbial that is an important driver of the biogeochemical cycles on which the functioning of earth depends. These soil microbial communities are vulnerable to environmental changes caused by human actions, including land use and climate change. However, our understanding of how shifts in microbial communities resulting from environmental change influences the global biogeochemical cycles they support is poor. This lack of knowledge is exacerbated by most studies investigating only one facet of environmental change: in the real world, human actions are causing multiple and simultaneous changes to the environment, including climate extremes that are expected to become more intense and frequent with on-going climate change. This is what this proposal is about: understanding how seasonally distinct climate extremes combine to impact soil microbial communities and the crucial biogeochemical cycles that they support. We do this in high mountain ecosystems, which cover a large part of the Earth's land surface, support high levels of biodiversity, and provide a host of services for humankind, including the storage of vast amounts of carbon, nutrients and water. Moreover, mountains are under considerable threat from climate and land use change. Climate change, for example, has been taking place in the mountains at almost double the rate of the northern hemisphere average, leading to less snow in winter, which reduces insulation of the ground and increases freeze-thaw activity, and less rain in summer, which causes prolonged drought. Yet, how these two factors combine to affect soil microbial communities, and is poorly understood. Furthermore, farming in mountains is also changing, with traditional grazing practices being abandoned in many mountains areas, which is causing encroachment of dwarf shrubs into the alpine zone. Put simply, mountain areas are at the front line of global change, but the consequences for microbial communities and the biogeochemical processes that they perform remain poorly understood.

Whilst soil microbes can often resist or recover from individual environmental perturbations, they may not be able to withstand multiple shocks happening in quick succession. Reduced snow in winter, followed immediately by severe summer droughts may tip soil microbial communities, and the nutrient cycling functions they perform, into alternative states. When such a shift occurs, the structure of the soil microbial community, and its capacity to cycle key nutrients will be permanently altered. Alarmingly, we do not know under which conditions such regimes shifts in microbial communities will occur, or whether changes in land-use practices will affect the outcome. Nor do we know what it will mean for global biogeochemical cycles, which is surprising considering the vast amounts of carbon stored in alpine soils, and the importance of nitrogen cycling for agricultural activities. This proposal tackles this issue head on, testing how reduced snow cover and summer drought affects the diversity and function of soil microbial communities and the consequences for biogeochemical cycles in these understudied ecosystems. We will tackle the following so far unexplored questions. Does one type of climate extreme impair the ability of soil microbial communities, and the biogeochemical cycles they support, to resist and recover from further perturbations? At what frequencies and severities of summer drought do microbial communities tip into an alternative state? Does encroachment of shrubs dampen the combined effect of seasonally distinct climate extremes on soil microbial communities? By testing these questions, we will gain novel, transformative understanding of the structure, function, and dynamics of microbial communities, and how this links to biogeochemical cycling, and we will do so in situ in the context of ongoing and rapid environment change in an understudied and vulnerable natural ecosystem.

(a) Who will benefit from our research?

The main beneficiaries of our research will be the academic community, via the generation of new fundamental knowledge on the consequences of climate extremes for soil microbial communities and major biogeochemical cycles in fragile alpine grasslands, and how effects are moderated by vegetation change. Our research, however, will also be of direct relevance to land managers and policy makers with interests in ecosystem service management in alpine regions and their resilience to climate extremes, which are expected to increase in their intensity and frequency with climate change. These key stakeholders include regional national park authorities in mountain regions and government environmental and conservation agencies, such as the environmental office of the Provincial Government of Tyrol, and farmers and landowners with interests in the management of alpine areas. Our project will also benefit the general public with interests in mountain ecosystems and threats to their biodiversity, including the large number of tourists who visit this region of Austria in both winter and summer.

(b) How will these benefits be realised?

Dissemination of research findings to international audience: This will be achieved through the publication of research findings in leading international journals, and via presentations by PDRA's and PI's at conferences and workshops. Given the novel and timely nature of our proposed research, and our track record of publishing high profile papers, we envisage that this proposal will yield several high impact publications. The PDRA will be encouraged to present at international conferences and workshops, and to be actively involved in research networks, such as the British Ecological Society (BES) Plants, Soils, and Ecosystems Special Interest Group (SIG) to disseminate research findings.

To engage with and promote knowledge transfer to stakeholders: We already have links with relevant stakeholders, including policymakers, land managers, farmers and landowners and the local and regional tourist office, via our NERC funded research in this regions. We plan to hold a one-day workshop for these stakeholders in autumn 2022, which will involve a series of presentations and discussions based on our findings. We also plan to involve a student intern in making a short film for the general public about threats of climate extremes in mountain ecosystems and potential solutions or mitigation strategies.

To raise public awareness of our research: the PI, Co-I and project partners have a strong track record of being actively involved in outreach activities, promoting public awareness of our science through local and national media interviews, and by presenting our results at science communication events. Here, a major focus will be on a public exhibition, during the winter ski season of 2021 in nearby Obergurgl, a popular ski resort, using artwork and instillations to inform the general public on the potential threats to ecosystem services of climate extremes in alpine regions. We will also take part in specific educational events at the Alpine Research Centre, Obergurgl (e.g. Summer School on Alpine Field Ecology) and public engagement meetings (e.g. University of Innsbruck "Open Science Days").

Transferable skills training: An important outcome of this project will be the delivery of a highly trained early career researcher and technician with training in multi-disciplinary approaches to the study of the soil microbiome, including cutting edge genomic tools and links to biogeochemical cycles. All staff will also receive training in advanced statistical approaches for analysing large datasets including network analysis, Bayesian modelling, and structural equation modelling. The Researcher Co-I will undertake public engagement training via NERC.