Experimental manipulations of soil fauna are a powerful tool for assessing causal relationships between belowground biodiversity and key ecosystem properties. However, there are technical difficulties in the preparation of soil microcosms for ecological experiments. One challenge lies in establishing treatments without soil fauna. Methods to exclude nematodes, an ubiquitous and functionally important component of soil biodiversity and ecosystems, have been developed for specific climate and soil types, often consisting in the application of nematicides that had interactive effects throughout the soil food web. Our goal was to remove nematodes from soils of three LTER ecosystems, ranging from desert to wet, without use of chemicals and with minimal disturbance. Three treatments were applied to 3-kg soil microcosms: (i) a 72-hours heating (65°C) - freezing (-20°C) - heating (65°C) cycle using soil in its original water content, (ii) heating (65°C) for 24h and (iii) 48h using soil that was pre-wetted to field capacity 24h prior heating. We measured treatments effects on total abundance and trophic structure of the nematode community. We then conducted a greenhouse experiment where individual seedlings of the dominant grass species for each site were transplanted to treated soils to investigate whether nematodes would recolonize 8 weeks after treatment.
A heat-freeze-heat cycle of 72h using soil in its original water content removed 60, 95, and 99% of the nematodes for the desert, semi-arid, and prairie soils, respectively. Pre-wetting soil increased mortality to 99% for all ecosystems after only 24h at 65°C. Plant-parasitic nematodes were the most resistant trophic group to the treatments. Eight weeks following the treatments, there was no significant nematode recolonization for the pre-wetted 48h heated soil, while there was a slight recovery in the soil from the 24h heating treatment. Thus, even though there was no significant difference in nematode mortality between times, 48h should be recommended for manipulative experiments longer than 8 weeks in order to assure the effectiveness of the treatments throughout the experiment. In conclusion, a nematode removal protocol in which soil at field capacity is left for 48h in an oven at 65°C killed 99% of the soil nematodes for three ecosystems from desert to humid grassland, and prevented recolonization of the nematode community for 8 weeks in the greenhouse, thus providing a tool for soil ecologists aiming at manipulative experiments on soil fauna.