Airborne fungal spore concentrations double but diversity decreases with warmer winter temperatures in the Brazilian Atlantic Forest biodiversity hotspot

Whilst research on climatic effects on fungal populations and communities (particularly of soil and litter-specialised species) has been done extensively, empirical examples of the impacts of climate change on airborne fungi are still lacking. Using a hot-air balloon to sample fungal spores during the winters of 2022 and 2023, here, we show the effects of warmer winter temperatures on airborne fungi in the Brazilian Atlantic Forest biodiversity hotspot. An increase of 1.36 and 1.85 °C in mean maximum and minimum winter temperatures of 2023 more than doubled the concentration of fungal spores in comparison to 2022, at the same time it did not affect the number of fungal species. Thus, there was a reduction in the diversity (Shannon Index – H’) of fungi in the atmosphere. Cladosporium sp. ranked in first, comprising 61 % of all spores collected and other important plant pathogens such as Epicoccum sp., Pithomyces sp., and Spegazzinia sp. had an increase in concentration of more than 4-fold with the warmer temperatures of 2023. Our results demonstrate how higher winter temperatures might impact fungal aerosols, suggesting that an increase in plant pathogens pressure is expected in a warmer world, with unknown consequences for climate regulation, crop production and the provision of ecosystem services. • Many methods detected an increase of at least 1 °C in winter temperatures of 2023. • Warmer temperatures of 2023 more than doubled the concentration of fungal spores. • Cladosporium sp. comprised 61 % of all spores and fungal diversity was reduced. • Phytopathogens increased up to 7-fold with the warmer temperatures. • Higher pressure of phytopathogens in the future with warmer conditions.