Rannveig M. Jacobsen, Anne Sverdrup-Thygeson, Håvard Kauserud, Sunil Mundra, Tone Birkemoe
Decomposition is the key to the cycle of life. Without decomposition, no nutrients are recycled from dead animals and plants, to be used by new organisms. In forests, a lot of nutrients and energy are bound in woody material. Fungi and invertebrates are the dominant eukaryotic organisms utilizing and decomposing dead wood. These decomposers are therefore vital to the functioning of forest ecosystems. Despite their importance, little is known of how invertebrates and fungi within dead wood influence each other, and how these interactions in turn influence the decomposition process.
We wanted to test the influence of wood-inhabiting invertebrates on fungi within dead wood. We constructed cages from a fine mesh net to exclude invertebrates from freshly felled logs. We combined this invertebrate exclusion treatment with uncaged logs as a control treatment, as well as logs within cages with cut holes (to control for microclimatic effects of the cage) and logs baited with ethanol. Ethanol has been shown to attract several wood-inhabiting invertebrates and would therefore function as a positive control. The logs were subject to these treatments for two years in the field. After that, we took wood samples for DNA-analysis to characterize the fungal communities, and for estimation of wood density to compare degree of decay.
The communities of fungi within the logs proved to be highly variable, and actually differed a lot between individual trees (even though all trees were of the same species and approximately the same age). However, when accounting for this variation, there was also a significant effect of treatment on composition of fungi within the logs. All treatments differed, but the logs with cages that excluded invertebrates differed most from the ethanol-baited logs presumed to attract large numbers of wood-inhabiting invertebrates. For instance, the wood decay fungus “turkey tail” (Trametes versicolor) was significantly more abundant in the ethanol-baited logs in comparison with the caged logs. We also found that wood density was lowest in the caged logs, which indicated that decay had progressed more slowly in these logs. Thus, our study strongly indicates that interactions between invertebrates and fungi in dead wood have significant effects on composition of decomposer communities and their function in forest ecosystems.