Recent advances in community and ecosystem genetics have shown that individual genotypes and genotypic diversity can have important consequences on communities and ecosystems.  Additionally, ecologists have long been interested in neighbor interactions as evidenced by decades of research into competition and more recently, facilitation. While a significant and growing body of literature has attempted to tie intraspecific genetic diversity to processes at the community and ecosystem level, very little is known about the consequences of inter- and intraspecific interactions between genotypes.  In 2007 we established a common garden to examine the community and ecosystem consequences of pairwise interactions between six genotypes of Solidago altissima and Solidago gigantea.  Each genotype was planted in monoculture and with each other genotype in a nearly full factorial design.  We compared the mean community and ecosystem responses for a genotype grown in monoculture to that same genotype grown with each other experimental genotype to examine additivity in response variables. Specifically, we hypothesized that a plant's neighbors would affect [1] aboveground net primary productivity (ANPP) throughout the growing season, and [2] pollinator visitation, richness, and community composition.

Results/Conclusions

ANPP and pollinator visitation varied [1] by species, [2] by genotype within S. altissima (but not S. gigantea), [3] by “neighbor diversity” (i.e. an S. altissima plant in monoculture receives only ~35% as many visits as an S. altissima plant with a neighbor of a different genotype of the same species, or a genotype of a different species), and [4] genotype-based neighbor effects (i.e. interactive effects of plant genotypic identity and neighbor genotypic identity, both within and between species). Pollinator community composition did not vary across genotypes, but it was affected by the overall genotypic and species diversity of the pot.  Although more productive plants received more pollinator visits in general, observed increases in pollinator visitation were not simply due to increased ANPP.  Even after accounting for differences in ANPP due to neighbor effects, S. altissima plants grown in non-monoculture pots received ~150% more visits from pollinators than did S. altissima plants grown in monoculture. In line with the results of previous studies, these results support the idea that inter- and intraspecific differences can lead to changes in communities and ecosystem properties. Additionally, the results show that genotypic variation between a plant and its neighbors can likewise affect communities and ecosystem processes.