As global change accelerates in the coming decades, wildfire disturbance events are predicted to increase rapidly both in rate and intensity. Severity and frequency of wildfires can fundamentally alter ecosystem functions. Many central ecosystem functions including biogeochemical cycling, hydraulic cycling, and soil fertility are mediated by the interactions between plants and root-associated soil microbes, therefore identifying how wildfire severity affects plant-soil microbe interactions is paramount to predicting plant-soil contributions to ecosystem services following fire disturbance events. Using soil collected from multiple sites of a burn gradient (unburned, low-moderate burn, high burn) produced by a 2016 wildfire in Great Smoky Mountains National Park, TN, we conducted two reciprocal transplant greenhouse experiments to a) assess plant functional trait responses to soil burn severity (first experiment using a common understory perennial Solidago flexicaulis) and b) assess the role of previous exposure to burn severity on plant colonist function (second experiment using seed of multiple Solidago species collected from sites across the burn gradient).
Results/Conclusions
S. flexicaulis individuals grown in high burn severity soil exhibited 10% faster relative growth rate of stem height compared to individuals grown in unburned soil (p = 0.02). S. flexicaulis individuals grown without field soil inoculum exhibited 9% and 13% faster growth rate compared to individuals grown with low-moderate burn severity soil (p = 0.03) and unburned soil (p = 0.002), respectively. S. flexicaulis yielded 9% greater leaf chlorophyll content in high burn severity soil compared to low-moderate burn severity soil (p = 0.03), and 11% greater leaf chlorophyll content when grown without field soil inoculum compared to individuals grown with unburned soil (p = 0.003). Solidago individuals from sites that experienced high burn severity grew 15% faster than individuals from sites that experienced low-moderate burn severity (p = 0.01). Solidago individuals from low-moderate burn severity sites flowered on average 1.5 months earlier than individuals from unburned sites (p = 0.02). Conversely, Solidago individuals from unburned sites produced 13% greater aboveground biomass compared to individuals from low-moderate burn severity sites (p = 0.05). These results could suggest that higher severity wildfire may reduce the presence of pathogenic soil microbes and contribute to enhancement of some plant functions through an enemy-release phenomenon. Subsequent amplicon and metagenomic sequencing of soil microbiomes of each burn severity soil inoculum will enable further understanding of how burn severity affects both soil microbial composition and function and the potential relationships between microbial function and plant function.