Experimental Manipulation of Precipitation Regime Affects Microbial Community Structure and Soil Carbon Storage in the Cold-Desert Sagebrush-Steppe
Spatial and temporal patterns of water availability link biological communities to atmospheric processes in semi-arid ecosystems. As a consequence of forecasted climate change, the seasonal timing and delivery of precipitation is predicted to change in the sagebrush-steppe of southeastern Idaho. We used a long-running ecohydrological experiment where soils have been supplemented (+200mm) with additional winter or summer irrigation (i.e., precipitation) for 17 years, asking if soil bacterial and fungal communities are structured by the historical precipitation regime. We used complementary molecular approaches to assess microbial community responses to sustained manipulation of precipitation-timing. We observed that precipitation-timing is a driver of bacterial community structure during the summer and fungal community structure during the winter. Bacterial and fungal community diversity metrics may be uncoupled from annual precipitation volume or timing. Still, our results suggest that the historical precipitation regime mediates the taxonomic abundance of prokaryotic and eukaryotic microbial communities in the sagebrush-steppe. Future changes in the seasonal timing of precipitation may restructure the composition of microbial communities observed at the 'phyla' and 'class' level of taxonomic resolution. Lastly, we observed that supplemental irrigation has reduced soil carbon storage by 14% relative to ambient conditions. Therefore, forecasted changes in the seasonal timing and delivery of precipitation will likely affect heterotrophic microbial community structure and ecosystem carbon storage in the cold-desert sagebrush-steppe.