Soil microclimate changes affect soil fungal communities in a Mediterranean pine forest

• Soil microclimate is a potentially important regulator of the composition of plant-associated fungal communities in climates with significant drought periods. Here, we investigated 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 during a 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.