REV I EW AND SYNTHES I S Global patterns in belowground communities

Noah Fierer,* Michael S. Strickland, Daniel Liptzin, Mark A. Bradford and Cory C. Cleveland Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO 80309, USA Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, USA Odum School of Ecology, University of Georgia, Athens, GA 30602, USA Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA 94720, USA School of Forestry and Environmental Studies, Yale University, New Haven, CT 06511, USA Department of Ecosystem and Conservation Sciences, University of Montana, Missoula, MT 59812, USA *Correspondence: E-mail: [email protected] Abstract Although belowground ecosystems have been studied extensively and soil biota play integral roles in biogeochemical processes, surprisingly we have a limited understanding of global patterns in belowground biomass and community structure. To address this critical gap, we conducted a meta-analysis of published data (> 1300 datapoints) to compare belowground plant, microbial and faunal biomass across seven of the major biomes on Earth. We also assembled data to assess biome-level patterns in belowground microbial community composition. Our analysis suggests that variation in microbial biomass is predictable across biomes, with microbial biomass carbon representing 0.6– 1.1% of soil organic carbon (r = 0.91) and 1–20% of total plant biomass carbon (r = 0.42). Approximately 50% of total animal biomass can be found belowground and soil faunal biomass represents < 4% of microbial biomass across all biomes. The structure of belowground microbial communities is also predictable: bacterial community composition and fungal : bacterial gene ratios can be predicted reasonably well from soil pH and soil C : N ratios respectively. Together these results identify robust patterns in the structure of belowground microbial and faunal communities at broad scales which may be explained by universal mechanisms that regulate belowground biota across biomes.