Background/Question/Methods Climate change and plant invasions are altering many environments world-wide, with potential consequences for soil microbial composition. To predict future trajectories of microbial communities, we must identify the dominant environmental controls over their structure. In the current study we constructed a phylogenetic tree with all published 18S and 28S rDNA soil fungal sequences in GenBank to determine how phylogeny, plant community type, soil type, precipitation, and temperature influence soil fungal distributions globally. We hypothesized that (1) fungal taxa are richer in lower latitudes, as has been observed in plants and animals; (2) fungal richness is highest at intermediate precipitation levels and temperatures due to competitive exclusion at higher levels and resource limitation at lower levels; and (3) if fungi are dispersal limited, geographic distance should be negatively correlated with community similarity; alternately, if fungi are highly dispersible, fungal communities in similar vegetation and soil types should be more similar due to habitat filtering.

Results/Conclusions Fungal richness was highest in temperate ecosystems. However, sampling effort was biased geographically towards these regions and was often too low to fully capture overall community richness. Fungal richness was significantly higher at intermediate temperatures and did not differ significantly with precipitation level. Geographically adjacent fungal communities were not more similar than expected by chance. However, fungal communities in comparable plant communities (i.e., forests or croplands) and soil types (i.e., Alfisols or Ultisols) were more similar than expected by chance. Additionally, fungal communities in agricultural and desert systems were more similar than expected by chance. Overall, this evidence suggests that fungi are capable of wide dispersal. Moreover, habitat filtering due to temperature, vegetation, and soil type significantly influences global soil fungal community composition. Since temperature and vegetation structure are altered by global change, global fungal distributions are likely to be affected as well.