Ecological and evolutionary consequences of genotypic variation and indirect genetic effects on plant-neighbor interactions

Most explanations for community structure exclude the effects of genes above the population level, but recent research suggests that distinct genotypes of dominant plant species can also play important roles in structuring associated communities and influencing ecosystem processes. However, very little is understood about how the outcomes of plant-neighbor interactions are determined by intraspecific genotypic variation and indirect genetic effects (IGEs), which are influences on the phenotype of a focal individual due to the expression of genes in an interacting individual. Using clones of both Solidago altissima and Solidago gigantea, we established two common garden experiments and a decomposition experiment to determine how genotypic variation and neighbor genotype (IGEs) affected a range of population, community, and ecosystem level responses. These included above- and belowground plant productivity and biomass allocation, plant chemistry, pollinator visitation, decomposition rate, and nutrient cycling. Combined, the results from the first common garden and decomposition experiment showed that IGEs changed belowground plant traits, and these changes also affected litter quality at the time of plant senescence. These shifts in litter quality extended to affect ecosystem processes, specifically decomposition rate and nitrogen (N) immobilization. This result shows that IGEs can initiate “afterlife effects”, linking aboveground-belowground interactions with evolutionary processes. Because IGEs strongly affected belowground plant traits in our first common garden, we established a second common garden which manipulated the presence of belowground interactions between neighboring plants. The goal of this garden was to test the hypothesis that IGEs are most important for traits related to acquiring limiting resources, which for our species was the supply of belowground nutrients. We found that IGEs explained over 20 times as much variation in focal plant belowground biomass than did focal plant genotype, but only in pots which allowed belowground interactions. To explore the importance of IGEs to questions at the interface of ecology and evolution, we also conducted a primary literature review which indicated that IGEs link ecological and evolutionary dynamics and that the consequences of this ecological-evolutionary linkage begin with the phenotype of an individual within a population and extend to the associated community and ecosystem.