Sex, bugs, & cuke ‘n' poll: aboveground seeds and belowground deeds

Background/Question/Methods The impacts of species interaction are often context-dependent, and vary with the nature of concurrent interactions. For plants, which interact with organisms both above- and belowground, these impacts may depend on other species' effects on either side of the soil surface, including both mutualists and antagonists. We examined the impacts of leaf damage by an aboveground herbivore on above- and belowground antagonists (folivores and root herbivores) and mutualists (pollinators and arbuscular mycorrhizal fungi) to determine how these interactions may alleviate or exacerbate the negative effects of herbivory on growth and reproduction in Cucumis sativus. We manipulated early-season leaf damage by a specialist herbivore and evaluated the role of pollinators in fruit production using a hand-pollination treatment. Results/Conclusions Early-season leaf damage had clear negative effects on plant growth and reproduction by reducing plant size, flower production, fruit production, and fruit weight. However, leaf damage increased seed production per fruit. Damage reduced the likelihood of later-season leaf damage by the same herbivore, suggesting defenses were induced, but had no effect on root herbivore abundance. However, recovery rates of root herbivores may have been too low to detect a response. Leaf damage treatments had no detectable effects on mycorrhizal colonization, suggesting that myccorhizae may have continued obtaining carbon from heavily-damaged plants, perhaps becoming carbon parasites and further reducing growth and yield. Increased damage reduced total pollinator visits, which may be expected given the low flower production on highly damaged plants, but the proportion of flowers visited was greater than on plants with low leaf damage levels. Plants appeared to be pollen-limited, but not in the traditional sense. Hand-pollination treatments increased fruit production, but fruit set (the proportion of female flowers that developed fruit) was not affected. Rather, plants with enhanced pollen receipt produced more female and male flowers. This pollen limitation was not affected by leaf damage, so pollinator visitation may have mitigated the negative effects of leaf herbivory.