Effect of fire severity and site slope on diversity and structure of the ectomycorrhizal fungal community associated with post-fire regenerated Pinus pinaster Ait. seedlings

We investigated the diversity and structure of the ectomycorrhizal (EM) fungal community associated with post-fire regenerated Pinus pinaster Ait., and the influence of fire severity and site slope on EM assemblage patterns. Seedlings were sampled in the first autumn and in both spring and autumn of the second growing season after fire, in a total of three samplings. EM percentages per seedling were assessed, morphotypes described, and tentative identification of EM types performed by restriction fragment length polymorphism (RFLP) and sequencing of nrDNA internal transcribed spacer (ITS) region. Seedlings were highly mycorrhizal in all samplings, independently of the factors studied. A total of 45 EM types were identified, and richness and diversity significantly increased from the first to the second autumn after fire. Neither fire severity nor slope had a significant effect on fungal richness and diversity. Overall EM community composition was similar in all samplings, although fire severity, site slope and elapsed time after fire caused evident shifts in presence or in relative frequencies of a number of EM types. No significant effect of fire severity or slope on EM assemblage patterns was detected in the first two samplings after fire. However, a significant effect of fire severity was observed at the end of the second growing season. The harvest of burned wood did not significantly affect EM fungal assemblages although the slope did. We conclude that there was a high potential of active EM inoculum in soil immediately after fire colonizing post-fire natural regenerated P. pinaster seedlings with high EM percentages, and that factors defining burn intensity, such as fire severity and topography, directly influenced the species composition and assemblage patterns of EM fungal communities, triggering replacements and succession of EM fungal species.