Cost-benefit Quantification of Leaf Carbon Economics to Disentangle Responses of Plant Assemblages to Deer Herbivory

Although the plant carbon cost-benefit balance is known to be related to individual plant growth, reproduction, and population expansion, the association with plant community differences is not well understood. In this study, we examined how the leaf carbon cost-benefit metrics were associated with the assembly process of forest understory plant communities in areas highly affected by deer browsing. We calculated these metrics from plant physiologically parameters for 14 forest floor plant species growing in deer presence/absence site to detect the relationship between species dominance and leaf carbon cost-benefit metrics. As a result, the patterns of interspecific variation in benefit along the plant dominance rank differed in deer presence/absence sites, contributing to the marked differences in species composition and diversity observed at the two sites. In the absence of deer, where competition was the dominant determinant of plant community composition, carbon benefits among species were positively related to the plant dominance rank, indicating that species able to acquire more carbon were at an advantage. On the other hand, under deer herbivory, differences in carbon benefit between species were not strongly apparent and were not related to the plant dominance rank, indicating few differences in reproductive and expansion ability (plant fitness) between species. This process contributes to the high species diversity of plant communities observed in the presence of deer. Our results emphasize the possibility of connecting different fields of studies, physiological ecology, community ecology, and the plant carbon cost-benefit balance of single leaves to explain plant community composition differences.