Canopy herbivory can mediate the influence of plant genotype on soil processes through frass deposition

The ecosystem consequences of intraspecific genetic variation is an emerging field of research that strengthens the link between population and ecosystem ecology. Despite recent advances, it remains unclear under what conditions (abiotic and biotic) plant genetic variation will be important to belowground processes. Forest canopy herbivores can have large influences on soil processes by altering the timing, quantity, and quality of forest floor inputs. We demonstrate that the frass inputs from canopy folivores (forest tent caterpillars and gypsy moths) reflect the intraspecific variation in green leaf chemistry (C:N, condensed tannins) of the aspen clones on which they fed. We then varied the genotype and nutrient availability of aspen and monitored the decomposition of both gypsy moth frass and senesced leaf litter in laboratory microcosms for 63 days. Aspen genotype influenced the short-term, frass-induced soil respiration as well as the longer-term, litter-induced respiration. In addition, aspen genotype interacted with nutrient availability to influence the activity of extracellular enzymes measured at the end of the experiment. These results suggest that in aspen forests, canopy herbivores can mediate the influence of intraspecific variation on ecosystem processes through frass deposition. Intraspecific variation is likely more important to ecosystem functioning than previously thought when trophic interactions are also taken into account. The potential for genetic variation within a single plant species to influence the ecosystem effects of herbivores highlights the importance of understanding how and when genetic variation matters to ecosystem processes.