Mycorrhizal traits inform dispersal and symbiotic function across scales

Bala Chaudhary, Department of Environmental Science and Studies, DePaul University, Chicago, IL, Carlos Aguilar-Trigueros, Freie Universität, Berlin, Germany and Matthias C. Rillig, Plant Ecology, Freie Universitaet Berlin, Berlin, Germany

Background/Question/Methods:
Plant-associated ecosystem functions and services are dependent on mycorrhizal associations, vital connections in ecology. These common root symbioses influence plant interactions across a range of organizational scales, from genes to ecosystems, and vary from mutualistic to parasitic depending on biotic and abiotic environmental context. Because the outcome of arbuscular mycorrhizal (AM) symbioses depends on fungal partner identity, understanding the drivers of AM fungal community assembly and biogeography improves our ability to predict mycorrhizal function and manage mycorrhizas in ecosystems. Arbuscular mycorrhizal (AM) fungi form belowground spores that differ substantially with respect to numerous quantifiable morphological traits. The ecological functions of these traits remains largely speculative, but spore traits could inform predictions regarding differential persistence, dispersal mechanisms, and host C sink dynamics among AM fungal species. Relationships between traits could inform potential energetic tradeoffs and AM fungal life history strategies. We built TraitAM, a database of quantitative AM fungal spore and life-history traits containing ~7k measurements from 314 original taxonomic species descriptions. Relationships among traits were explored and linkages between spores traits and mycorrhizal function are investigated. We asked: 1) Do trade-offs exist between spore traits that inform dispersal and mycorrhizal symbiotic economies? 2) Can spore traits predict symbiotic function to hosts in arbuscular mycorrhizas?
Results/Conclusions:
Using AM fungal spore size and spore wall thickness data, we calculated spore wall investment, a species-specific metric that indicates differential investment in resources related to propagule protection from decomposition in the soil environment, UV radiation during aerial dispersal, or degradation during animal dispersal. We observed evidence of a tradeoff between spore size and wall investment such that AM fungal species with larger spores invest fewer resources in protective walls. This resource tradeoff exists despite larger spores requiring thicker walls for allometric structural integrity, and despite the fungal partner using carbon acquired from a symbiotic host. Using data from MycoDB, a global meta-analytic mycorrhizal function database, the relationship between spore traits and plant symbiotic function is explored. Mycorrhizal trait data and relationships between functional traits can inform predictions regarding life history tradeoffs, which could have implications for a spore economic spectrum and inform mycorrhizal function.