Soil fauna in cold ecosystems: climate change, interactions and ecosystem functioning

A square meter of tundra soil can contain over a million soil animals and uncountable bacteria and fungi. These soil organisms are omnipresent, are tremendously diverse and are known to play a major role in carbon turnover by constantly ingesting, excreting and respiring part of this carbon by feeding on dead organic material. Still, soil organisms are not taken into account when predicting to what extent carbon emissions from cold regions may increase under climate change.

The cold northern region provides one of its most important services by storing about twice the amount of carbon that is currently in the atmosphere in its soils. Climate warming will most likely stimulate the release of a large part of the carbon from these soils, which may reinforce climate warming. One of the processes responsible for this is the breakdown of dead organic material by soil organisms (decomposers). Decomposer soil organisms ingest organic carbon and nitrogen during their feeding activities and release it again by excreting non-organic nitrogen and respiring carbon dioxide. Within the decomposer community, fungi and bacteria are responsible for the breakdown of the smallest particles of organic material and most of the respired carbon dioxide, whereas soil fauna, such as springtails, mites and worms, fragmentize larger organic material into smaller particles, but simultaneously feed on the bacteria and fungi; thereby affecting microbes both positively and negatively. The net outcome of these interactions will eventually determine the efficiency of the breakdown process and consequently the release of carbon from soils. A major difficulty in predicting the magnitude of carbon release from cold soils under climate warming is that, although the direct effects of temperature on biochemical processes are fairly well studied, its effects on these soil organisms, and how they interact with each other, are still largely unknown.

In my research, I focus on studying decomposer soil fauna, such as springtails, mites and (earth) worms in cold, arctic, alpine and boreal ecosystems. I study how these organisms respond to environmental changes as well as the consequences of these responses for ecosystem functioning. I am particularly interested in studying the whole soil food web, including interactions between soil fauna, bacteria, fungi and plants. Moreover, I try to unravel how changes in such interactions may explain unexpected effects of environmental changes on carbon and nitrogen cycling.  I do this by identifying soil communities using both traditional methods (microscope) and metagenomics (DNA) and combine this community information with measurements of carbon and nitrogen cycling.  My hypothesis-driven research approaches range from using controlled laboratory studies and field (climate) manipulation studies, to frequent field observations across time and space, which are needed to study soil organism impacts on larger scales.

In my docent lecture, I will show how climatic changes may directly (via changes in soil temperature and moisture) or indirectly (via responses of other organisms) affect soil decomposer communities and the consequences it may have for ecosystem functioning. Furthermore, I will demonstrate that climate-change driven soil organism ‘invasions’ in previously un-colonized habitats can have dramatic effects for plants and carbon and nitrogen cycling. Finally, I will discuss the importance of sampling soil organisms frequently in time and space, and highlight my future research lines.