Ph.D. in Soil fauna physiology

The project was started August 2005 with Ph.D. student Kristine Maraldo. The project is linked to WP 2.2, but includes elements of work packages 3 and 4 as well. The focus will be on desiccation tolerance in protozoa, nematodes, enchytraeids, Collembola and mites.

Background
Soil invertebrates are important components of soil ecosystems. This diverse group of animals covers a range of taxa, the most important being protozoans, nematodes, oligochaete worms (earth-worms and enchytraeids), mites, springtails (Collembola) and a range of insects (mostly belonging to Diptera and Coleoptera) whose larval stages complete their development in the soil. Soil inverte-brates perform important functions in soil related to the growth conditions of plants. Soil meso-fauna, for example represented by enchytraeids, mites and Collembola, are grazers of bacteria and fungi, and are thought to stimulate microbial decomposition rates. At present there seems to be a consensus that the respiration of soil invertebrates amounts to little more than 10% of the total soil respiration (bacteria and fungi being the dominant biotic components), and often less than this. However, the indirect effects on soil respiration and decomposition, though difficult to quantify, may be substantial. A number of examples is showing that soil fauna may increase nitrogen miner-alisation with up to 25%.

One of the most important environmental factors determining the performance of soil fauna is the availability of water in the soil. In essence, there are three survival strategies open to soil fauna species during drought. Firstly, they may have evolved the ability to tolerate extensive loss of body water. The most extreme case of this is termed anhydrobiosis, a strategy utilized by nematodes and some collembolans. Secondly, they may have evolved resistance to desiccation by reducing the water permeability of their integument. This strategy has been adopted by many surface-dwelling species, whereas euedaphic species have little or no control of evaporation across the integument. Finally, species may migrate to moist micro-sites during drought periods, either vertically or horizon-tally. This last strategy may enable species to evade transient drought spells but longer lasting or extreme drought is likely to incur physiological stress.

Project description
The main focus of this Ph.D. project will be on drought tolerance in soil fauna, preferably within enchytraeids and microarthropods. The studies should elucidate by which mechanisms selected organisms cope with low soil water potentials, identify critical stress levels and examine life-history traits under sub-optimal soil water potential. Also population recovery times after severe drought should be investigated. The main body of the project will be laboratory based experimental studies, but participation in field studies of soil mesofauna is also included using the CLIMAITE long-term field trial as a platform. Together, these studies should help to increase our understanding of soil fauna population and community responses in a changing climate.

This Ph.D. project will have close interactions with other parallel CLIMAITE projects on plant physiology, plant community changes, microbiology, microfauna-plant interactions and biogeochemistry.