Sonoran Desert Soil Microbial Community Responses to Changes in Precipitation Regime

Abstract

Changes in patterns of precipitation are anticipated across the Western United States and globally in the face of climate change. Climatological models predict that rainfall events in many areas, including the Sonoran Desert, will become larger and more intense but less frequent in the coming years. The impacts of these changes on microbial community composition and function remain uncertain. Here, we examine the effects of a range of summer precipitation regimes– from many, small rainfall events every 3-5 days to a climate change regime with very few, very large rainfall events every 21 days– on microbial community composition and function. Adapting Grime’s competitor, stress tolerator, ruderal (CSR) life history strategy framework for microbes, we had hypothesized that microbial communities would shift in composition to favor drought tolerant taxa, reduced extracellular enzyme activities, and reduced growth as a response to prolonged desiccation stress under the climate change summer monsoon precipitation regime. Contrary to our expectations, we find that microbial community composition and extracellular enzyme activities vary little under modified summer precipitation. However, microbial biomass is reduced by as much as 25 percent under a climate change regime with very few, very large rainfall events and long dry periods between events. This reduction in microbial biomass could help to explain reductions in seasonal soil carbon efflux previously observed under this regime. Our results suggest that desert soil microbial communities and their associated biogeochemical activities may be more resilient than expected in the face of changes to precipitation regimes caused by climate change. Our results also suggest that Grime’s CSR framework should be applied only with caution to microbial communities in global change research– not all changes in climate will lead to changes in microbial communities' exposure to stress, especially in communities already adapted to extremes.