Print PageDecomposition of organic matter in forest soils is a complex process where both fungi and bacteria participate. The differences between litter and soil reflecting the different chemistry of organic compounds contained within are likely to affect the relative importance of individual bacterial and fungal groups in decomposition. The aim of this study was to identify bacteria and fungi active in decomposition with a special emphasis on cellulose and hemicellulose hydrolysis. To achieve this, characterization of microbial community was done by pyrosequencing of soil DNA and RNA and combined with stable isotope probing and the activity of extracellular enzymes (EEA) was analyzed.
Results/Conclusions
In Picea abies forest soil sampled in winter, during the period where decomposition processes dominate, microbial communities of different horizons differed considerably in their species composition. Bacterial communities (>20 000 OTUs) were dominated by Acidobacteria, Proteobacteria and Actinomycetes, while fungi (>1000 OTUs) mainly belonged to Ascomycetes and Basidiomycetes. While ectomycorrhizal fungi strongly dominated the DNA pool (>80%), the active community was enriched in saprotrophic fungi. Transcript pool of fungal cellobiohydrolase (exocellulase) cbhI was found to contain 80 different genes in the H horizon and 150-200 genes in the litter horizon, approximately. Out of the genes present in the metagenome, 40% were transcribed in the L horizon and 25% in the H horizon. Interestingly, some of the most abundant transcripts were produced by fungi with very low abundance in the ecosystem. cbhI genes showed distinct association with either the L or H horizons and indicated that different fungal communities decompose cellulose in different soil depths. The analysis of genes involved in hemicellulose and pectin decomposition also showed that the communities of their producers are highly diverse. Analysis of microbes actively decomposing 13C-cellulose showed a clear distinction of their community from the total community and also confirmed the fact that cellulose degradation is performed by different microorganisms at different soil depths. The results also show that there are many important cellulose-degrading microorganisms which were earlier not recognized as such including some mycorrhizal fungi and Acidobacteria. Microorganisms with low abundance are likely highly important in decomposition processes. The relative ratio of fungal to bacterial biomass in soils along a pH gradient was found to affect the properties of extracellular enzymes which points at the functional specificity of these two groups. Bacterial and fungal decomposer communities are highly diverse, specific for particular soil horizon and functionally different.
