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

Seasonal variations in ectomycorrhizal symbiosis of Quercus ilex trees were studied, with special emphasis on tree health status, Phytophthora cinnamomi root infections and topography. Five Q. ilex forests in western Spain were selected, and ca. 40 000 root tips from 3 declining and 3 non-declining trees per forest were examined. 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 by P. cinnamomi root infections but by topography. Abundance of Russula spp. was not influenced by P. cinnamomi root infections but by the decline status of trees. The relationships found between tree physiology and ectomycorrhizal abundance changed significantly depending on the decline status of trees. For the first time, seasonal variations in ectomycorrhizae in P. cinnamomi-infected Q. ilex forests are reported. The low diversity and abundance of ectomycorrhizal fungi associated with declining trees should be further studied in order to uncover causes or consequences of Q. ilex crown transparency.