Impacts of ramet density and herbivory on floral volatile emissions and seed production in Solidago altissima

Premise

Plants produce an array of floral olfactory and visual cues to attract pollinators, including volatile organic compounds (VOC), which mediate plant–pollinator interactions and may be influenced by herbivory and neighboring plants. Consequently, these factors may affect plant fitness by disrupting pollination. However, most evidence comes from controlled experiments, limiting our understanding of how VOCs function in natural populations. This study investigated how herbivory and conspecific ramet density influence floral VOC profile, pollination, and seed production in a naturally occurring population of Solidago altissima.

Methods

We recorded leaf herbivory and ramet density surrounding one focal ramet in 1-m² plots. We collected VOCs from the floral headspace and measured ovary fertilization as a proxy for pollination success and the number of seeds produced by the focal ramet.

Results

Our findings revealed interactive effects between ramet density and herbivory on floral VOC emission, richness, and diversity. Specifically, at lower ramet densities, herbivory did not affect floral volatile emissions. However, in highly dense stands, herbivory suppressed floral volatile emissions. Despite these changes, floral volatiles did not affect pollination and the number of seeds in S. altissima.

Conclusions

Our field-based findings underscore the importance of understanding the complex responses of floral VOCs to environmental stressors and their contributions to plant reproduction within natural communities. Our results suggest that while herbivory and ramet density influence floral scent, these changes do not affect reproduction in our study. Ultimately, generalist-pollinated plants like S. altissima might not rely heavily on chemical signaling during pollination.