Fire recurrence effects over the structure and activity of ectomycorrhizal fungal communities in Mediterranean pine forests

Abstract

Fire is an intrinsic factor of Mediterranean forest ecosystems, determinant of abiotic disturbance and organism¿s ecology. Wildfire recurrence and predicted increase associated with global change may particularly alter the fertility and microbial communities of soil. Symbiotic ectomycorrhizal (EM) fungi are main actors of forest soils, directly involved in the cycling of nutrients and the productivity of trees. We surveyed forests of two representative Mediterranean pines, Pinus pinaster Ait. (Ppi) and Pinus halepensis Mill. (Pha), to evaluate whether fire recurrence affected the structure and functioning of EM fungal communities. Ectomycorrhizal root tips of both pine species were collected in low and high fire recurrence forest sites, measured for enzymatic activities (EAs) involved in geochemistry cycles and nutrient mobilization, and fungal identification approached by high-throughput sequencing. Fire recurrence significantly altered the assemblage of EM fungi, while the community richness remained unaffected. EAs secreted by EM fungi highly diverged depending on the tree species, being generally greater in the rhizosphere of Pha compared with that of Ppi. High fire recurrence negatively impacted the activity of the Ppi ectomycorrhizas, whereas in the case of Pha, most EAs were unaffected. A general increase of laccase activity, involved in the oxidation of various substrates, such as phenols or lignin, was observed in recurrently burned areas. Fire recurrence effects might be explained through the divergent altered edaphic properties and specific fungal community composition of the forests studied, which could have relevant implications on decomposition rates, carbon storage, and availability of nutrients in soils, finally affecting the productivity of Mediterranean forest ecosystems. 247