Stream environmental conditions are homogenised outside a protected area, but fungal beta diversity remains unchanged

Matter and energy fluxes and ecosystem services in streams rely on fungi associated with leaf litter. However, the species diversity of this microbial group may differ between a protected area and its surroundings. Thus, to understand how beta diversity may depend on the conservation status of an area, we aimed to evaluate the structure and diversity (α, β, and γ) of the aquatic fungal community from a subtropical area and how it is distributed in streams from a protected area and from a farmland area. Hence, we compared eight streams inside with eight streams outside of a protected area. This is one of the first studies testing the biotic homogenisation hypothesis for fungi associated with leaf litter in streams. We found new records of fungal species from a global biodiversity hotspot. The gamma diversity of aquatic fungi was surprisingly high. Our analyses indicated a process of environmental homogenisation of streams outside the national park. Intriguingly, neither α nor β diversity differed between areas. Environmental variables presented large differences, especially regarding nutrients, which influence the aquatic fungal community. Altogether, this national park seems to be effective in protecting the environmental heterogeneity of streams to some extent; however, the national park was likely suffering from pollution, which requires further investigation.