Effect of different levels of collembolan grazing on interspecific competition between microfungi, decomposition of organic matter and bio-availability of nitrogen

Summary

The effect of selective grazing by a collembolan (Folsomia fimetaria) on the reproduction and ability to degrade wheat straw by 2 species of microfungi was measured. The experiment was performed with 3 different grazing pressures and a control without grazing. The 3 grazing pressures correspond to an initial density of 10.000, 20.000 or 100.000 collembolans/m2. The density cannot however be directly related to a field density, because the soil column was only approximately 2 cm high.
Results show that the most preferred fungus to F. fimetaria, Alternaria infectoria, were only affected in terms of reproduction at the highest grazing pressure of 30 collembolans (as initial density). Both respiration rates and the content of bio-available nitrogen in the microcosms containing A. infectoria either alone or in competition with Mucor hiemalis, at all grazing pressures, showed that the fungus was very resilient to grazing.
M. hiemalis reproduced most, respired most and retained most bio-available nitrogen at a grazing pressure of 6 F. fimetaria (initial density) compared to 3 or 30 collembolans as initial density. Apart from this there was no effect of collembolan grazing on reproduction.
The results suggest that A. infectoria and M. hiemalis are able to avoid competition in this study, as a result of different ecological strategies.