Seasonal variations of ectomycorrhizal communities in declining Quercus ilex forests: interactions with topography, tree health status and Phytophthora cinnamomi infections

Abstract

SeasonalvariationsinectomycorrhizalsymbiosisofQuercusilextreeswerestudied,withspecialemphasisontree health status, Phytophthora cinnamomi root infections and topography. Five Q. ilex forests in western Spain were selected,andca.40 000roottipsfrom3decliningand3non-decliningtreesperforestwereexamined.Ectomycorrhizal fungal abundance and P. cinnamomi root infections were quantified seasonally for 2 years, and an assessment was made of the water soil content and physiological status of trees during summer, the most stressful season. Seasonal changes in ectomycorrhizal fungal abundance were higher for Tomentella spp. than those for Russula spp. and Cenococcum geophilum, but these changes were not influenced by topography, tree decline status and P. cinnamomi root infections. Seasonal variations of non-vital tips were conditioned significantly by the decline status of trees. A higher proportion of non-vital tips and a lower proportion of vital non-mycorrhizal tips were observed in declining than in non-declining trees. Abundance of C. geophilum and Tomentella spp. was not influenced byP. cinnamomi root infections but by topography. Abundance of Russula spp. was not influenced byP.cinnamomirootinfectionsbutbythedeclinestatusoftrees.Therelationshipsfoundbetweentreephysiology and ectomycorrhizalabundance changed significantly depending on the decline status of trees. For thefirsttime, seasonal variations in ectomycorrhizae inP. cinnamomi-infectedQ. ilexforests are reported. The lowdiversityand abundance of ectomycorrhizal fungi associated with declining trees should be further studied in order to uncover causes or consequences of Q. ilex crown transparency.