Soil fungi are key drivers of terrestrial carbon cycling, yet our understanding of how fungi will respond to forecasted climate remains limited. There is an expectation, for example, that soil fungi are drought tolerant, but few studies have directly tested this assumption beyond the short-term. Here, we hypothesize that fungal responses to moisture and drought are constrained by historical conditions, whereby climate legacies determine the ability of fungi to respond to changes in water availability. Alternatively, fungi may closely track contemporary water availability and shift abundance and composition to match. To address the relative importance of historical and annual precipitation on soil fungi, we measured soil hyphal networks and community composition across a steep rainfall gradient in central Texas over a decade. Additionally, we examined how fungal abundance shifted in experimental microcosms with soils from historically drier and wetter regions of the same rainfall gradient exposed to a range of water availabilities in the lab for one year.
In soils across the Texas gradient, historical rainfall was the primary controller of fungal community composition, with only a small effect of contemporary weather. In contrast, fungal abundance increased as a function of current soil moisture, with only a small carryover effect of rainfall in the previous year and no effect of historical rainfall. When moisture was manipulated in microcosms, fungal abundance reflected the interaction of historical and current conditions – soils from historically wetter sites generally had more abundant hyphae, and this was most apparent at higher moistures. Overall, these findings are consistent with historical precipitation regime acting as a strong filter on fungal species. However, observed legacies on composition were largely independent of overall soil fungal abundance, with only limited constraints under controlled conditions and small year-to-year legacies. The underlying relative abundance dynamics are not currently known, but could shed light on whether overall fungal communities respond to moisture in concert or whether individual taxa respond differentially. Understanding long-term dynamics of soil fungal community composition and abundance in the context of historical and future environmental variation may provide us with a framework for improving prediction of ecosystem responses to climate change.