BAAR, JACQUELINE, VICKY VALINLUCK & TOM BRUNS.
Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720, U.S.A.
In October 1995 a wild fire burned approximately 13,000 acres of forests and chaparral at Point Reyes National Seashore. Included in the burnt area were three 35-40 year Pinus muricata forest sites where the pre-fire ectomycorrhizal community has been described. All trees at the three sites were killed by the fire and P. muricata seedlings regenerated abundantly within a few months after the fire. From February to May 1997, about 250 P. muricata seedlings were harvested from the three sites to characterize the below-ground mycorrhizal flora. Mycorrhizal root tips were morphotyped and the biomass of each type was determined. PCR/RFLP analysis and nucleotide sequencing were applied for identification of the types. Fire-induced changes in mycorrhizal species composition were striking: from dominance of Tomentella sublilacina and Russula species in the pre-fire mycorrhizal community to dominance of Suilloid fungi (Alpova and Rhizopogon spp.) and Ascomycetous fungi (Tuber and Wilcoxina spp.) in the post-fire community. Two years after the fire sporocarps of mycorrhizal fungi were observed for the first time. These included Amanita gemmata, Boletus chrysenteron, Chroogomphus vinicolor, Coltricia perennis, Hebeloma crustuliniforme and a clavarioid fungus. Some taxa, such as Suilloid and Ascomycetous fungi, were present in the soil as spores prior to the fire as demonstrated by pre-fire bioassays. Other taxa, e.g. C. perennis and H. crustuliniforme, were not observed either in the pre-fire community or in pre-fire bioassays. These species likely dispersed by wind after the fire. Remaining taxa were known resident of the pre-fire community, but were not observed in bioassays. Survival of mycelium seems to be their mechanism of establishment. Mycorrhizal species composition above- and below ground differed significantly between the three sites and spatial distribution of the mycorrhizal fungi was patchy. Species composition and patchiness will be related to (a)biotic factors.