Ecologist’s Diary with Rob Mills: Making the most of summer snow

It’s late July, the alpine meadows of the Swiss Alps are in full bloom, and the heat of the summer sun drives a deep sweet smell from the litter of the spruce forest floor as we start our walk up. My friend and colleague Mark leads the way as we move up the tour de Mont Blanc from la Fouly in the Valais, heading for our research site at ~2500m. There, the sun has given rise to abundant flowers, rich meadows, the buzzing of insect and bird life, but still works hard at melting the last of last of the snow. As we reach the site, we are greeted with the familiar, but always astounding, mixture of snowbeds, ridges, meadows, flush wetland, pools and screes of this dynamic and fantastic environment (see picture).

The alpine landscape at 2500m.
The alpine landscape at 2500m.

This spatial heterogeneity, driven by the complex topography and the resultant hydrology (mainly snow cover and drainage), insolation, and to some extent by the degree of clay accumulation, is one of the wonders and great challenges of this environment. For the ecologist and biogeochemist, understanding the ecosystem-forming factors, their rate of change, and ultimately, their sensitivity to global change, is a significant challenge. In our work, we are especially interested in three angles: 1. How do the microbial communities and their C cycling dynamics vary across alpine landscapes; 2. Are there stoichiometric connections across the soil-microbe-plant continuum; 3. Do microbial communities from contrasting alpine microhabitats exhibit differing sensitivity to climatic extremes.

Summer of 2017 saw us collecting soil and vegetation samples to address points 1 and 2 in this case-study landscape. We chose initially to focus on the end-members of the landscape: the late-melting snowbeds and the dry ridges, as we have very little baseline understanding of the microbial functioning of these landscapes. The within-system variance is large, and from the photos, you can see how ridge systems, with a mixture of gramminoid, forbs and even dwarf shrubs, differs from the snowbeds, which move across a successional scale from mosses, through Rannunculus, to Salix. A major challenge is therefore assessing how generalisable such categorical variables (i.e. snowbed) can be in understanding soil-plant interactions.

Examples of the vegetation in ridges (left) and snowbeds (right).
Examples of the vegetation in ridges (left) and snowbeds (right).

Back in the lab, the vegetation sorted, dried and ground for elemental analysis, we concentrate on the microbial functions. With Dr Kate Buckeridge at Lancaster, we are getting to grips with the carbon use efficiency, using isotopically-labelled microbial necromass, and are exploring the expression of extra-cellular enzymes, before finally probing the structure of the microbial community. This all paves the way for summer 2018, where we will use this baseline data on structure and function to go more broadly across the system, and explore the sensitivity of the microbial community to extreme events such as drought and high rainfall. As water-towers of the world, land for food production, and large reservoirs of diversity, we need to understand the nature of our mountain systems, and crucially, how soils will respond to change. As part of this work, we are forming a network of snowbed studies. Interested? Drop me a line and get involved.

Dr Robert Mills, @mountainecology

Read more Ecologist’s Diary or more posts by Rob Mills.

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