Soil microbial community dynamics and biogeochemical cycles under global change: effects of climate and vegetation change in alpine ecosystems

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Scientists are becoming increasingly aware that that highly diverse microbial communities in soil play major roles in driving the biogeochemical cycles on which the functioning of Earth depends. It is also becoming clear that this belowground microbial diversity is highly sensitive to land use and climate change, but the consequences of this for biogeochemical cycling are poorly understood. This is what this proposal is about: understanding how both land use and climate change work together to influence soil microbial communities and their functioning, and to experimentally test the consequences of this for major biogeochemical cycles. Uniquely, we do this in high mountain ecosystems, which cover a large part of the Earth's land surface and provide a host of services for mankind, including the storage of vast amounts of carbon, nutrients and water. Moreover, mountains are under considerable threat from climate and land use change, but the consequences of this for biogeochemical cycles is largely unknown. Climate change, for example, has been taking place in the mountains at almost double the rate of the northern hemisphere average. Also, there is considerable concern that land use change, especially the collapse of traditional farming, will have major impacts on how mountain ecosystems function. Given all this, coupled with new knowledge nutrient cycles of mountain ecosystems rely on tight coupling between soil microbial and plant communities, it is all the more surprising that the consequences of global change for soil microbial diversity and the functioning of mountain ecosystems remains largely unexplored. One of the most noticeable impacts of climate change in mountain areas is less snow, especially in spring. This reduction in snow is happening at an alarming rate, and there is concern that it will accelerate in future years, potentially reducing snow cover by around 50% at the end of this century. On top of climate change, the way that mountains are farmed is also changing, with traditional grazing practices being abandoned in many mountains areas of the world. A consequence of this, which is compounded by climate change, is the encroachment of dwarf shrubs into the alpine zone. New research shows that both of these changes, namely reductions in snow cover and the encroachment of dwarf shrubs, can have dramatic affects on the way that mountain ecosystems function. But the concern is that when they happen together, the impacts are magnified. This proposal tackles this issue head on, testing how shrub encroachment and reduced snow cover simultaneously affect the diversity and activity of soil microbial communities and the consequences for biogeochemical cycles in these understudied ecosystems. We will tackle the following so far unexplored questions. Do reductions in snow cover disrupt the growth and activity of soil microbial communities across the year, both in summer and winter, and does this alter the cycling of carbon and nutrients, and supply of nutrients to plants? Do these changes in soil microbial communities have legacy effects in the future, reducing their ability to deal with other affects of climate change, such as summer drought, which is also increasing in alpine areas? Finally, does the encroachment of shrubs dampen, or amplify, the effects of reduced snow cover on ecosystem processes by altering microclimate and promoting the growth of more resilient fungi in soil? By testing these questions, we will not only yield novel, transformative understanding of the structure, function, and dynamics of microbial communities, and how this links to biogeochemical cycling, but we will do so in situ in the context of ongoing and rapid environment change in an understudied and vulnerable natural ecosystem. Our studies will also provide policy makers and land managers with guidance on how best to manage mountain ecosystems to maintain their integrity in the face of rapid climate and land use change.