Patterns and drivers of wood-decaying fungi diversity at global scale

Background/Question/Methods

In the majority of species groups, species richness increases from the poles towards the equator, known as the latitudinal diversity gradient (LDG). The observed LDGs were often attributed to climate, niche conservatism, and evolutionary radiation and extinction rates. The global diversity patterns of fungi are only known from soils. Overall they contrast the LDG but differ among guilds. Wood-inhabiting fungi have not been studied yet, despite their importance as main decomposers for carbon sequestration and release. Local studies found wood-inhabiting fungi to be highly host-specific; hence their diversity correlates strongly with host tree diversity. Environmental factors like macro- and microclimate are of minor importance. Since the tropics harbor the most host tree species diversity on earth, we expect wood-inhabiting fungi diversity, in contrast to soil fungal diversity, to follow the LDG. We set up a global dead wood experiment within major biomes across six continents. At each plot, we exposed three standardized dead-wood objects of local common tree species. We characterized the fungal communities based on metabarcoding technique and analyzed alpha and beta diversity on plot- and dead-wood object-level and gamma diversity among biomes.

Results/Conclusions

Gamma diversity of rare and common species was slightly higher in the tropics than in temperate forests, while dominant species diversity was not different. The boreal biome harbored the smallest gamma diversity. Contrastingly, alpha diversity at the plot and dead-wood object-level was highest in boreal forests. Beta diversity among dead-wood objects and host tree species contributed most to total diversity, while continents and biomes played a minor role. Models revealed the mean pairwise phylogenetic distance of host tree species as an important factor explaining these patterns. Despite higher tree species diversity in the tropics than in boreal systems, wood-inhabiting fungi diversity does not follow the LDG, in contrast to the majority of other taxa groups but in accordance with soil fungi. Host identity seems more important for global wood-inhabiting fungal diversity than biome differences like macroclimate, resource availability, and host tree diversity. Hence climate change-induced changes in tree diversity would affect wood-inhabiting fungal diversity and decomposition processes stronger than the actual climatic alternations.