PS 47-215 - Fungal Evolution in Response to Chronic Soil Warming

Abstract: Chronic soil warming alters fungal-mediated soil carbon (C) cycling, but the evolutionary mechanisms underlying these interactions remain unclear. Forest soils represent an important C sink, but future climate warming is expected to shift forest soil C cycling and the biological communities that facilitate these processes. Warming accelerates plant-litter decomposition and increases C loss, and this response is mediated by saprotrophic fungi via decomposition. Soil warming alters fungal community structure and shifts decomposition dynamics, though it is unclear whether these functional shifts are the result of altered community structure, phenotypic plasticity (easily-reversible changes in single generations or individuals), or evolution (multi-generational adaptation in response to selective pressures). Soil warming induces long-term functional changes in soil fungi, but evidence of selective mutations has not been shown. Another global change stressor, atmospheric nitrogen deposition, induced non-plastic functional adaptations in the wood-decomposer Irpex lacteus. Because evolution ultimately shapes the long-term fate of fungal communities, understanding how warming drives evolutionary processes in saprotrophs can enhance our ability to predict long-term forest C storage. We therefore examined whether sustained soil warming induces directional selection of functional traits, and therefore evolutionary adaptation, in soil saprotrophs. We hypothesized that chronic soil warming induces non-plastic, functional adaptations in these fungi (H1) and that these adaptations are correlated with genomic variation (H2). To test H1, we conducted a common-garden experiment examining the effects of soil warming on 1) the growth rate and 2) the plant-litter decay ability of I. lacteus. We isolated I. lacteus individuals from three artificial soil warming treatments at the Harvard Forest Long-term Ecological Research (LTER) site: control (no warming), short-term warming(16 years), and long-term warming (20 years). We then incubated these isolates in leaf-litter microcosms and quantified litter mass loss and fungal biomass production at multiple time points. To test H2, we conducted a transcriptomic analysis. We extracted RNA from each leaf litter microcosm used in the first experiment, quantified differential gene expression, and compared sequence variation in genes expressed differentially among treatments. Results indicate that long-term, but not short term, soil warming increases the ability of these fungi to decompose plant litter. Our results suggest that chronic soil warming fundamentally alters fungal decomposition dynamics, with significant consequences for forest ecosystems and the planet.