In fire-frequented habitats plants producing pyrogenic fuels generate feedbacks on fire characteristics, thereby engineering fires that maintain fire-dependent ecosystems. Soil fungi also affect fuels directly by altering litter decomposition and indirectly by affecting plant diversity and productivity, with effects varying among functional groups. Fungi also vary in susceptibility to fire, so fire may drive specific changes in fungal communities, producing predictable effects on fuels and the probability of future fires. We developed a conceptual model for “fire-fungal feedbacks” based on fire severity, then conducted a field experiment to compare differences in 1) fungal communities, both in litter and soil, and 2) decomposition of new litter between recently burned and unburned (2 years) sites in an old-growth pine savanna (Wade Tract). Because pines host different symbiotic fungi than grasses and their recalcitrant litter produces hotter fires, experimental treatments also included sampling sites in the vicinity of pines or 10+ meters from pine overstory. Litter and soils were collected and high-throughput DNA sequencing of all fungi was used to analyze differences in fungal communities. Decomposition of new, site-specific litter (sterilized via gamma irradiation) was assessed using litter bags (30 µm mesh to exclude non-microbes) collected 5, 8, and 11 months after fire.
Results/Conclusions
Fire shifted fungal communities, eliminating some species and facilitating others. Sequencing of the ITS2 region produced 12,882 fungal OTUs identified (>5 reads), 65% were shared between burned and unburned patches, 24% were restricted to unburned patches, and 12% to burned patches. Community differences between burned and unburned patches were greater in litter than surface soil layers. Fire eliminated fungi in the Basidiomycota and increased the abundance of Ascomycota that dominated litter. Fungal communities were not distinct near or away from pines, possibly because fungi from pines and herbaceous plants overlapped at the spatial scale sampled. Five months after fire microbial decomposition of new litter was ~40% greater in unburned than burned sites and this difference remained after 11 months. Slower post-fire decomposition of new litter will increase fine fuel accumulation the year after fire, a positive feedback likely to decrease return intervals of fires necessary to maintain fire-frequented ecosystems. Our data indicate that fungi are integral components of fire-frequented ecosystems. Ongoing research will be discussed to assess the role of fire suppression in shifting this fungal component and their potential fire adaptation as a necessary tool in restoring fire-dependent ecosystems.