The Ecological Factors that Structure the Composition and Function of Saprotrophic Fungi: Observational and Experimental Approaches.

Abstract

A central goal in ecology is to understand the processes underlying the distribution and abundance of species at local, regional and global scales. As mediators of biogeochemical cycles, understanding the mechanisms that govern microbial community assembly are of ecosystem-scale significance, yet they remain a critical gap in our ecological knowledge. Through a combination of observational and experimental approaches, I explored the roles of selection, drift and dispersal in structuring microbial communities of saprotrophic fungi at a variety of spatial and temporal scales. Furthermore, I investigated the link between fungal community composition and functional characteristics in order to understand whether the factors that structure microbial community assembly have direct consequences to ecological function. First, I explored the role of selection in structuring soil microbial community assembly along a secondary successional chronosequence. My work revealed that the accumulation of organic matter and change in plant litter biochemistry during plant succession (10 to 86 yrs following agricultural abandonment) shaped saprotrophic fungal composition and their physiological potential to metabolize plant detritus, providing support for the idea that changes in plant communities have direct outcomes on the competitive dynamics of saprotrophic microbial communities in soil. Secondly, I found that both dispersal limitation and drift had a persistent effect on the phylogenetic structure and functional richness of saprotrophic fungal communities across a long-term glacial chronosequence (9,500 to 13,500 yrs following glacial retreat). Last, I manipulated initial colonizers and leaf litter biochemistry to understand the relative importance of priority effects and selection in structuring saprotrophic fungal communities and leaf litter decay. I found that the strength of priority effects was dependent on leaf litter biochemistry and physiological traits within a regional species pool. Together, these findings demonstrate that selection, drift and dispersal structure fungal community assembly at both local and regional levels with important consequences to plant litter decay. Furthermore, my observations provide support for the assertion that the same ecological forces structuring plant and animal communities also shape the assembly of saprotrophic fungi.