Productivity Drives Leaf Mycobiome Diversity Patterns at Global and Continental Scales

Abstract

Aim: Studies assessing large-scale patterns of microbial diversity have predominantly focused on free-living microorganisms, often failing to link observed patterns to established theories regarding the maintenance of global diversity patterns. We aimed to determine whether foliar fungi on two closely related grass hosts—Heteropogon contortus and Themeda triandra—display a commonly observed latitudinal gradient in species richness and determine whether host identity, energy (temperature and precipitation), climate seasonality, fire frequency and grass evolutionary history drive the observed patterns in species richness and composition. Location: Paleotropical. Time Period: Contemporary. Major Taxa Studied: Foliar fungi. Methods: Foliar fungal diversity was quantified from 201 leaf samples of T. triandra and H. contortus collected across the distributional range of these species. Mixed effects models were used to quantify patterns of diversity and their correlates among and within continents. Ordinations were used to assess drivers of composition. Results: Foliar fungi displayed consistent latitudinal diversity gradients in richness. Energy was a strong driver of richness at inter-continental and continental scales, while other factors had inconsistent impacts on richness among scales, hosts and guilds. Globally, richness was higher in regions of higher growing season temperatures and where hosts were present for longer periods. Composition was primarily structured by geographic region at the global scale, indicating that distance was a dominant driver of community composition. Within Australia, temperature and rainfall seasonality and the amount of growing season rainfall, were the dominant drivers of both richness and composition. Main Conclusions: We find some support for the idea that foliar fungal species diversity is governed by the same factors as many macro-organisms (energy availability and evolutionary history) at inter-continental scales, but also that fungal diversity and composition in the highly seasonal continent of Australia were driven by factors that shape tropical grassy ecosystems, namely climate seasonality and fire.