Physiological responses of the soil fauna –
Work package 2.2

Studies of a few species have shown that the soil fauna is able to tolerate adverse environmental conditions, such as drought and low temperatures by various physiological adaptations, e.g. accumulation of low molecular weight carbohydrates to increase body fluid osmolality (Bayley and Holmstrup 1999; Holmstrup et al. 2002). Despite these adaptations, low water potential in summer and low winter temperatures yet limit the activity of the soil fauna (Rapoport and Tschapek 1967; Holmstrup 2002) and are therefore likely to affect the function of organisms and possibly re-structure community composition. On the other hand, warmer and moister winters are likely to increase faunal decomposing activity and therefore increase the flux rates of C and nutrients from the soil organic matter. Because primary production and the retention of nutrients in plant biomass are limited during winter, the increased activity is likely to increase leaching losses of plant C and nutrients from the ecosystems.

In order to quantify the contribution of soil fauna to decomposition and plant nutrient mobilizations, critical levels of soil moisture and temperature for the activity of selected soil organisms will be identified and the persistency of the effects at the community and population level will be examined. We will focus on responses in protozoans, nematodes, collembolans, mites and enchytraeids that represent various trophic levels and that are likely to play the most significant role for ecosystem functioning. Hence, the chosen combination of species will make it possible to extrapolate responses of key species and functional groups to community responses.

The main work will be related to the field scale treatments, but in order to establish response patterns and functional relationships between the soil fauna and the environmental changes, the field experiments will be combined with laboratory studies under controlled temperature and moisture conditions. These will include analyses of detailed physiological responses to desiccation and temperature extremes including growth rates, reproduction, physiological acclimation processes and costs of acclimation in terms of reproduction and longevity. With these experiments it will be possible to identify critical intensities and duration of drought and temperature extremes of the selected species. The responses will also be measured as effects on the respiratory activity in the laboratory using flow-through respirometry, with particular emphasis on responses at periods of low, but not limiting, winter temperatures. These measurements will give indications also of the litter decomposition and microbial grazing. The results will be extrapolated to field conditions using the monitoring of soil moisture and temperature of the field plots, and the population size data obtained in WP3.

The outcome of the research will be used for generating rules of response patterns for various functional groups of soil fauna subjected to a number of climate change scenarios. This knowledge is to be used in the overall task of predicting ecosystem responses to climate change (WP5) – especially to the increased length of growing seasons and to predictable changes of within-season fluctuations of weather events.