Abstract
Few studies have comprehensively investigated the temporal variability in soil microbial communities despite widespread recognition that the belowground environment is dynamic. In part, this stems from the challenges associated with the high degree of spatial heterogeneity in soil microbial communities1 and because the presence of relic DNA2 may mask temporal dynamics. Here we disentangle the relationships among spatial, temporal, and relic DNA effects on microbial communities in soils collected from contrasting hillslopes in Colorado, USA. These sites were chosen because they have distinct soil microbial communities and experience strong seasonal changes in precipitation and temperature regimes. We intensively sampled plots on each hillslope over one year to discriminate between temporal variability, the intra-plot spatial heterogeneity, and relic DNA effects on the soil prokaryotic and fungal communities. We show that the intra-plot spatial variability in microbial community composition was strong and independent of relic DNA effects and these spatial patterns persisted throughout the study. When controlling for intra-plot spatial variability, we identified significant temporal variability in both plots, particularly after relic DNA was removed, suggesting that relic DNA hinders the detection of important temporal dynamics in soil microbial communities. We also identified microbial taxa that exhibited shared temporal responses and we show that these responses were often predictable from temporal changes in soil conditions. These findings highlight approaches that can be used to better characterize temporal shifts in soil microbial communities, information that is critical for predicting the environmental preferences of individual soil microbial taxa and identifying linkages between soil microbial community composition and belowground dynamics.