COS 131-3 - Ectomycorrhizal colonization of Populus tremuloides is a function of genotypic and environmental factors

Abstract: Due to their highly context-dependent nature, mycorrhizal symbioses have been challenging to integrate into broader frameworks of biogeochemical cycling and global change. The current distribution of ectomycorrhizal (EM)-associated trees closely correlates with increased soil organic matter and nitrogen limitation, which is thought to be a result of the unique ability of EM fungi to access nitrogen from organic matter. Differences in litter (leaf and root) chemistry of associated host trees in combination with these functional attributes of EM fungi could lead to feedbacks promoting the success of the EM strategy. These feedback loops are currently receiving more attention in the mycorrhizal literature and are thought to contribute to broadscale processes of nitrogen and carbon cycling. However, given that global changes are expected to affect both above and belowground processes, determining which factors are important to the maintenance of these feedback loops is critical to understanding how these systems might change in the near and distant future.



This study aimed to determine whether environmental, genetic, or a combination of these factors influenced mycorrhizal colonization in aspens (Populus tremuloides), and whether any variation attributed to tree genotype could be further explained by tree phenotypic traits that modify the local biogeochemical environment. To assess this, a field experiment was conducted at the WisAsp common garden in Arlington, Wisconsin. Roots, leaves (live and abscised), and soil samples were collected from 2-4 replicates of 30 P. tremuloides genotypes and were subjected to chemical analysis. We predicted that mycorrhizal colonization would vary across genotypes of P. tremuloides and that there would be positive phenotypic and genetic correlations between leaf and/or root litter quality and EM colonization.



Preliminarily results indicate that ~25% of the phenotypic variation in EM colonization was explained by tree genotype (broad sense heritability of ~0.25) and that genotypes with more recalcitrant abscised litter (higher C:N) had greater EM colonization irrespective of environment. Additionally, colonization was negatively correlated with C:N of the surrounding soil. None of the leaf chemistry traits measured in this study correlate with soil C:N, though root C:N could be a potentially contributing factor (p=0.098). Collectively, this indicates that colonization is a function of genetic, phenotypic, and environmental factors and that tree chemistry has the potential ability to promote feedback loops involved in N acquisition. This study supports our predictions that EM colonization varies with P. tremuloides genotype and is linked to phenotypic traits that may modify the soil environment.