Which forest soil fungi cope best with summer drought?

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Soil microclimate may be an important regulator of plant-associated fungal community composition in climates with substantial drought periods. This study investigated how soil fungal communities varied across space and time in a Mediterranean Pinus pinaster forest in relation to soil moisture and temperature.

In a year-long spatio-temporal observational study, researchers collected 336 soil samples monthly over 1 year from 28 long-term experimental plots. They assessed fungal communities using PacBio sequencing of ITS2 amplicons, estimated total fungal biomass by analysing ergosterol, and analysed community changes in the context of functional traits.

Soil fungal biomass was lowest in summer and late winter and highest in autumn, when mycorrhizal species also had a greater relative abundance. Within the year, changes in community composition across space and time were significantly correlated with soil moisture and temperature.

Mycorrhizal fungi were less affected by summer drought than free-living fungi. Specifically, 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.

These observations indicate the potential for shifts in both the composition and function of 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.