PhD Defence Elsa Arrazola Vasquez

Opponent: Dr. Pia Euteneuer, University of Natural Resources and Life Science, Vienna, Experimental Farm Gross-Enzersdorf, Schlosshoferstrasse 31, 2301 Gross- Enzersdorf, Austria

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Summary/Abstract of the PhD thesis

Soil compaction has a key role in shaping earthworm burrowing activity. Understanding the impacts of soil conditions (e.g. soil moisture, soil compaction) on earthworm burrowing is important to foresee the effects on soil functions driven by earthworm activity. This thesis investigated the effects of soil compaction on earthworm burrowing, using different earthworm species. Effects on burrowing rates and burrowing modes, as well as on energy costs for burrowing, were analysed. Also, the temporal dynamics of earthworm burrowing were examined by exposing earthworms to different initial soil conditions under semi-field conditions.

The effects of compaction were adverse, with a significant reduction in burrowing rates at higher soil compaction levels, from 13.5 cm d-1 to 5.8 cm d-1 and 6.5 cm d-1 to 3.6 cm d-1, for A. caliginosa and A. longa, respectively. In compacted soils, soil ingestion was the main burrowing mode for earthworms. Earthworms tended to spend about 50% more energy to burrow in compacted soils, which could be detrimental in terms of their long-term energy requirements. An analysis of the temporal dynamics of earthworm burrowing under semi-field conditions showed that earthworm burrowing rates were in the range between 1 and 4 cm3 d-1 while casting rates were between 1.3 and 3.3. cm3 d-1 and the fraction of ingested soil increased towards autumn, after 24 weeks. The data suggest that burrowing is a function of the interaction effects of soil compaction and moisture level, with stronger negative impacts in moist-compacted soils.

This thesis found that soil compaction reduces significantly the burrowing rates and increases the energy costs for the burrowing of earthworms. In addition, the temporal burrowing dynamics showed that even with different soil initial conditions, earthworms burrowing seems to be similar in their mean burrowing rates, mean casting rates and burrowing mode, after six months.