Microbial communities and their relevance for ecosystem models: Decomposition as a case study

Soil microbial communities are so vastly diverse that complex interactions, which alter ecosystem functions, mayoccuramongmicrobial species and functional groups. In this review,weexplore the empirical evidence for situationswhen shifts in the communitystructureofmicrobeswouldelicit a change inecosystemprocess rates, specifically decomposition, even when microbial biomass remains constant. In particular, we are interested in a subset of these scenarios in which knowledge of microbial community structure would improve model predictions for ecosystem functions. Results frommicrocosm and field studies indicate that microbial species diversity, functionalgroupdiversity, andcommunitycompositioncanall influenceecosystemprocess rates. The underlying mechanisms that may elicit changes in ecosystem functions from shifts in microbial community structure include evolutionary constraints onmicrobial trait adaptation, trait correlations, dispersal limitation, and species interactions. The extent of microbial diversity in soils is not known, so it is presently not possible to model all scenarios of microbial community structure shifts. However, by incorporating documented patterns in functional groups that are relevant for a particular ecosystem process and potential relationships between microbial phylogeny and function, the predictive power of process models will be significantly improved.The inclusionof this information intoprocessmodels is critical forpredictingandunderstandinghow ecosystem functions may shift in response to global change. 2009 Elsevier Ltd. All rights reserved.