PS 78-194
Moth defoliation causes a shift in root and soil fungal communities
Above- and belowground parts of forest ecosystems are tightly connected via carbon and nutrient cycling between green plants, their fungal symbionts and other heterotrophic soil organisms. It is therefore likely, that removal of tree canopy foliage due to herbivory will have a major impact on soil fungi. During 2004-2008, mountain birch forests (Betula pubescens ssp. czerepanovii ) in subarctic Fennoscandia suffered from extensive, successive defoliations by larvae of autumnal moth (Epirrita autumnata) and winter moth (Operophtera brumata). We investigated the responses of fungal communities in soil and in mountain birch roots to natural moth defoliation at three levels of moth defoliation (intact control, full defoliation in one season, full defoliation in two or more seasons), replicated in three distinct localities. Fungal communities in birch roots and in adjacent soil were studied with 454 pyrosequencing and ion semiconductor sequencing of tagged amplicons of the ITS2 rDNA region.
Results/Conclusions
Moth outbreak reduced mountain birch survival to 50% and nearly zero after one and several defoliations, respectively. Consequently, defoliation caused significant changes in functional and taxonomic community composition of soil and root-associated fungi. In birch roots fungal communities shifted from dominance of Basidiomycota to Ascomycota, while an opposite pattern was detected in soil. In the roots this was due to loss of basidiomycetous mycorrhizal fungi, whereas in soil saprotrophic Basidiomycota became more common after defoliation. Furthermore, moth defoliation altered the functional composition of fungal communities. Symbiotic mycorrhizal fungi declined in abundance and in richness, especially in roots showing a reduction of 70-80%, while saprotrophs and root endophytic fungi increased after moth defoliation. Our results highlight the importance of carbon flow from green hosts as a key driver of belowground fungal communities and suggest a marked role of aboveground herbivores in shaping soil fungal communities.