Will free-living microbial community composition drive biogeochemical responses to global change?

Abstract

Microbes carry out many critical biogeochemical transformations in the biosphere such as greenhouse gas production and consumption. Characterizing how microbial communities vary through space and time may hold insights into understanding ecosystem function, particularly as it responds to ongoing climate change. However, it remains unclear to what extent variability in the composition of microbial communities exerts long-term control over biogeochemistry independently of the physiochemical and macroorganismal context in which microbes reside. In this synthesis, we reviewed literature about the versatility and adaptability of microbial communities, and analogous research in medicine, agriculture, and bioremediation. We synthesized data from microbial diversity experiments to determine thresholds at which loss of microbial richness impairs function and compared it to actual microbial richness in nature. The evidence suggests that, in environments such as surface soils, sediments, rivers, lakes, oceans, and the atmosphere, which are open to microbial inoculum and which dominate biogeochemical processes in the biosphere, microbial function equilibrates to environmental conditions over a much shorter interval (days to years) than the time scale on which anthropogenic climate change influences ecosystems (decades to centuries). We conclude that the degree of microbial control over ecosystem processes has been overstated because the correlation of taxonomic information with ecosystem function has obscured the understanding of causality in natural ecosystems. We recommend experiments in which microbial communities are manipulated in ways that allow us to disentangle the influence of microbial community structure from confounding environmental covariates.