Life history determines biogeographical patterns of soil bacterial communities over multiple spatial scales A. BISSETT,* A.E. RICHARDSON,* G. BAKER,† S. WAKELIN‡§ and P. H. THRALL* *CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2601, Australia, †CSIRO Entomology,GPO Box 1700, Canberra, ACT 2601, Australia, ‡CSIRO Land and Water, Environmental Biogeochemistry, PMB 2, Glen Osmond, SA 5064, Australia, §AgResearch, Lincoln Research Centre, Private Bag 4749, Christchurch 8140, New Zealand Abstract The extent to which the distribution of soil bacteria is controlled by local environment vs. spatial factors (e.g. dispersal, colonization limitation, evolutionary events) is poorly understood and widely debated. Our understanding of biogeographic controls in microbial communities is likely hampered by the enormous environmental variability encountered across spatial scales and the broad diversity of microbial life histories. Here, we constrained environmental factors (soil chemistry, climate, above-ground plant community) to investigate the specific influence of space, by fitting all other variables first, on bacterial communities in soils over distances from m to 10 2 km. We found strong evidence for a spatial component to bacterial community structure that varies with scale and organism life history (dispersal and survival ability). Geographic distance had no influence over community structure for organisms known to have survival stages, but the converse was true for organisms thought to be less hardy. Community function (substrate utilization) was also shown to be highly correlated with community structure, but not to abiotic factors, suggesting nonstochastic determinants of community structure are important Our results support the view that bacterial soil communities are constrained by both edaphic factors and geographic distance and further show that the relative importance of such constraints depends critically on the taxonomic resolution used to evaluate spatio-temporal patterns of microbial diversity, as well as life history of the groups being investigated, much as is the case for macro-organisms. Keywords: bacteria, biogeography, soil, species-area relationships Received 4 March 2010; revision received 21 July 2010; accepted 23 July 2010 Introduction Understanding processes underlying the generation and maintenance of spatial patterns in biodiversity is a fun- damental goal of ecological research. Numerous studies have revealed the patterns of general importance, such as latitudinal gradients and species–energy relation- ships, that relate to species richness, particularly for macro-organisms (Gaston 2000). However, the extent to which variation in microbial communities is structured by stochastic or deterministic processes, and how these link to variation in local environmental parameters (physicochemical environment, climate, overlying plant community and disturbance regime) or evolutionary events, is still poorly understood. Microbial biogeogra- phy has been the subject of several recent reviews (Green & Bohannan 2006; Hughes-Martiny et al. 2006; Ramette & Tiedje 2007a) which have highlighted the importance of understanding microbial communities in the light of current ecological theory primarily devel- oped from studies of macrobial communities. Neverthe- less, there is still considerable debate regarding the applicability of general ecological theories to microbial communities. With regard to the role that spatial heterogeneity plays in structuring microbial communities, results from previous studies are conflicting, fuelling debate in Correspondence: Dr Andrew Bissett, Fax: 612 624 64820; E-mail: Andrew.Bissett@csiro.au Ó 2010 Blackwell Publishing Ltd Molecular Ecology (2010) 19, 4315–4327 doi: 10.1111/j.1365-294X.2010.04804.x