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Biodiversity at many scales (functional group, species, genetic) can result in emergent ecological patterns. Here we explore the influence of tree genotypic variation and diversity on in-stream ecosystem processes and aquatic communities. We test whether genetically diverse inputs of leaf litter interact with a keystone organism, anadromous salmon, to influence in-stream ecosystem function. We used reach-level manipulation of salmon carcasses and leaf litter bags to examine how nutrient inputs interact with genetic variation in leaf litter decomposition. Genotypic variation in black cottonwood (Populus balsamifera ssp. trichocarpa) significantly influenced leaf litter chemistry, litter mass loss, and fungal biomass, but these variables were only weakly influenced by salmon carcass presence or a genotype × salmon (G × E) interaction. Mixtures of genotypes tended to demonstrate antagonistic effects (slower than expected decomposition) in the absence of salmon, but synergistic effects (faster than expected decomposition) when salmon were present. Our findings suggest that the influence of plant genotypic variation in linking aquatic and terrestrial ecosystems may be altered and in some cases intensified in the presence of a keystone vertebrate species.

Recent studies have shown effects of host plant genetics on community and ecosystem processes, which makes understanding the impacts of genetically based traits on hidden or non-apparent organisms more important. Here we examined links among genetic variation in hybrid cottonwoods, plant phytochemistry, and twig fungal endophytes (i.e., a common hidden organism). We found three major patterns: (1) twig fungal endophyte infection was positively related to the introgression of Fremont cottonwood (Populus fremontii S. Wats.) RFLP genetic markers, (2) condensed tannin concentration in twig bark tissue was negatively correlated to the introgression of Fremont genetic markers, and (3) fungal endophyte infection was negatively related to condensed tannin concentration in twig bark. These data demonstrate that plant genotype can impact hidden ecological players (i.e., fungal endophytes) resulting in community and ecosystem consequences.Key words: ecological genetics, fungal endophytes, hidden players, hybridization, Populus, tannins.