Fungal Response to Fire and Implications for Carbon Dynamics in Forest Ecosystems.

Fungi play a critical role in carbon (C) cycling in forest ecosystems both through decomposition of organic C and by forming mycorrhizal associations with plants. Fire is the primary disturbance in these systems and the response of fungal communities to fire has implications for C dynamics. Fire affects fungi directly by causing mortality or indirectly by altering soil conditions. Pyrogenic carbon (PyC) – burned C material produced from biomass combustion – is a product of fire and has been shown to change the soil environment by transforming organic labile C into resistant C. Due to the extent to which fungi mediate C cycling through ecosystems, it is critical to understand the relationships between fungi, fire, and PyC and consequences for ecosystem processes. Increased PyC has been shown to increase water retention, alter soil nutrient dynamics and modify soil structure. These disturbance-induced differences in the soil environment may affect the ability of fungal communities to recover after fire. We conducted a comprehensive meta-analysis of studies investigating the direct impact of fire on fungal communities. We also preformed an observational study investigating fungal biomass and PyC in non-burned, moderately and severely burned Ponderosa pine forests after a wildfire in the Poudre Canyon of northern Colorado. We used FDA and Calcoflour fluorescent staining techniques to determine active and inactive fungal biomass. Benzene polycarboyxlic acid (BPCA) molecular markers were isolated from soil samples to quantify PyC content in the litter and soils. Fungal biomass was also compared to other biotic and abiotic soil factors (pH, nitrogen content, total C content, temperature, moisture, respiration, and enzyme activity). We determined the relative importance of PyC content as a driver of fungal biomass in fire-disturbed forest ecosystems using a multivariate approach. We present our results describing the relationship between fungal activity and PyC content along a fire intensity gradient.