Linking composition to function in soil microbial communities - current thinking and future directions

Background/Question/Methods General laws in ecology should apply to organisms of all taxonomic groups.  However, it is questionable whether traditional approaches to studying effects of community composition on ecosystem processes can be applied to microbial communities.  We are ultimately interested in understanding patterns of ecosystem processes at landscape scales, at which “microbial communities” encompass thousands, perhaps millions, of taxa with hidden spatial distributions.  Many of these microbial taxa can play a similar ecological role, potentially resulting in a high degree of functional redundancy.  We will provide thoughts on some new theoretical, experimental, and technological approaches that may help relate microbial communities to ecosystem processes, before highlighting our case study.  Previously, we had proposed that molecular analyses of microbial communities would be more closely linked to ecosystem processes by examination of specific functional genes that mediate ecosystem processes, as well as taxonomic markers.  Here, we will describe our efforts to apply this approach to understand extracellular enzyme activity and decomposition in northern temperate hardwood forests. 

Results/Conclusions Attempts to relate functional genes to ecosystem processes have been hampered by unexplained variation that confounds extrapolation to the landscape scale.  We have investigated spatial patterns in community composition and functional traits in order to both investigate the causes behind this unexplained variation, and to quantitatively account for unexplained variation at larger scales.  In addition to analysis of functional gene abundance and composition, we have found that shifts in gene expression may be a key driver of ecosystem processes.  This raises the prospect of physiological plasticity of individual microorganisms being as important as functional redundancy within the soil microbial community.  Finally, a mismatch in phylogenetic resolution between functional and taxonomic genes represents a fundamental barrier to relating functional genes to taxonomic community composition and diversity, and organismal physiological ecology.