Soil microclimate is a potentially important regulator of the composition of plant-associated fungal communities in climates with significant drought periods. Here, we investigated the spatio-temporal dynamics of soil fungal communities in a Mediterranean Pinus pinaster forest in relation to soil moisture and temperature. Fungal communities in 336 soil samples collected monthly over 1 year from 28 long-term experimental plots were assessed by PacBio sequencing of ITS2 amplicons. Total fungal biomass was estimated by analysing ergosterol. Community changes were analysed in the context of functional traits. Soil fungal biomass was lowest during summer and late winter and highest during autumn, concurrent with a greater relative abundance of mycorrhizal species. Intra-annual spatio-temporal changes in community composition correlated significantly with soil moisture and temperature. Mycorrhizal fungi were less affected by summer drought than free-living fungi. In particular, mycorrhizal species of the short-distance exploration type increased in relative abundance under dry conditions, whereas species of the long-distance exploration type were more abundant under wetter conditions. Our observations demonstrate a potential for compositional and functional shifts in fungal communities in response to changing climatic conditions. Free-living fungi and mycorrhizal species with extensive mycelia may be negatively affected by increasing drought periods in Mediterranean forest ecosystems.

Containerized Pinus pinea L. seedlings are commonly used for reforestation in the Mediterranean area. While there is an increasing knowledge of the potential ectomycorrhizal fungi associated with Pinus pinea, few studies exist of inoculation techniques with selected ectomycorrhizal fungi. We tested seven ectomycorrhizal fungi for their effectiveness with containerized Pinus pinea seedlings. Hebeloma crustuliniforme, Laccaria laccata and Pisolithus tinctorius were applied as vegetative inocula while Melanogaster ambiguus, Pisolithus tinctorius, Rhizopogon luteolus, Rhizopogon roseolus and Scleroderma verrucosum were tested as spore inocula. The inoculum of each fungus was tested at several application rates. Among the fungi tested as vegetative inocula, the highest percentages of ectomycorrhizas were obtained with H. crustuliniforme at all rates tested. The ectomycorrhizas formed by L. laccata varied from 11% to 40% depending on the inoculum rate applied. Vegetative inoculum of Pisolithus tinctorius was only effective at the highest inoculum rates and gave mycorrhization percentages around 60%. Pisolithus tinctorius applied as a spore inoculum formed ectomycorrhizas at a frequency of about 50% at the effective inoculum rates. The rest of the fungi applied as spore inocula produced more than 50% of ectomycorrhizas at the effective spore concentrations. These included the highest percentages of ectomycorrhizas (>80%) obtained with both Rhizopogon species. Differences in growth due to inoculation with the different fungi were not detected and in some cases inoculation even reduced the total biomass accumulated by seedlings. All seedlings reached a size suitable for transplantation.

Summary Thirty‐four fungal species isolated from cork oak (Quercus suber) in Catalonia (NE Spain) during 1992–95 were tested for pathogenicity either in stem, leaf or root inoculations. Eleven species were found to be pathogenic on stem: Biscogniauxia mediterranea, Botryosphaeria stevensii, Diatrype cf. stigma, Endothia gyrosa, Fusarium solani, Graphium sp., Ophiostoma quercus, Phomopsis sp., Phytophthora cinnamomi, Sporendocladia bactrospora and an unidentified Coelomycete. Three fungi showed pathogenic effects on leaves: Dendrophoma myriadea, Lembosia quercina and Phomopsis quercella. No clear pathogenic effects were detected in the root inoculation experiment. Trunk pathogens were differentiated into two groups according to the effects induced in the inoculated plants; B. stevensii, Phomopsis sp. and P. cinnamomi caused the death of the inoculated plants and induced the formation of large cankers and vascular necroses. The other pathogenic species also produced severe cankers and vascular lesions, but no significant mortality was detected. Water stress increased the lesions caused by B. mediterranea and Phomopsis sp., but limited those of P. cinnamomi and the rest of the inoculated fungi. However, water stress did not significantly affect the damage caused by B. stevensii, which was the most virulent of the species tested. Leaf pathogens only showed their effects if the leaf cuticle was previously damaged. Lembosia quercina caused small dark lesions whereas D. myriadea and P. quercella produced large necrotic areas in well‐watered plants. The lesions caused by the last two fungi were reduced by water stress.

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