Agricultural soil legacy influences multitrophic interactions between crops, their pathogens and pollinators.

Soil legacy influences plant interactions with antagonists and below-ground mutualists. Plant-antagonist interactions can jeopardize plant-pollinator interactions, while soil mutualists can enhance plant-pollinator interactions. This suggests that soil legacy, either directly or mediated through plant symbionts, affects pollinators. Despite the importance of pollinators to natural and managed ecosystems, information on how soil legacy affects plant-pollinator interactions is limited. We assessed effects of soil management legacy (organic versus conventional) on floral rewards and plant interactions with wild pollinators, herbivores, beneficial fungi and pathogens. We used an observational dataset and structural equation models to evaluate hypothesized relationships between soil and pollinators, then tested observed correlations in a manipulative experiment. Organic legacy increased mycorrhizal fungal colonization and improved resistance to powdery mildew, which promoted pollinator visitation. Further, soil legacy and powdery mildew independently and interactively impacted floral traits and floral reward nutrients, which are important to pollinators. Our results indicate that pollination could be an overlooked consequence of soil legacy and suggests opportunity to develop long-term soil management plans that benefit pollinators and pollination.

Plant susceptibility to a shared herbivore is reduced by belowground competition with neighbors.

Spatial variation in plant community composition is an important driver of variation in susceptibility to herbivores. In close proximity, certain neighbors can attract or repel herbivores to a focal plant ("associational effects"). Neighboring plants may also compete for resources, modifying their phenotype in ways that affect susceptibility to herbivores. To test whether and how competition contributes to associational effects, we manipulated the sharing of belowground resources among plant neighbors (spotted Joe Pye weed and common boneset) that serve as alternate hosts for an herbivorous beetle. In the field, the beetle Ophraella notata laid more eggs and inflicted more damage on plants of both species that were released from belowground competition with neighbors. Competition also weakened the effects of neighbor identity during field trials, reducing associational susceptibility. When beetles were forced to choose between the two host species in cage trials, competition again reduced beetle use of Joe Pye weed as a secondary host. To test the role of plant traits related to herbivore defense and nutrition, we quantified leaf protein, specific leaf area, and trichomes, and conducted behavioral assays on leaf disks. Beetles did not distinguish between Joe Pye weed treatments at the leaf disk level, and competition did not impact specific leaf area and protein. Trichome density was higher in both species in the preferred treatment. Overall, our results suggest that belowground interactions between plants may mediate the strength of associational effects, as secondary hosts become more attractive when released from competition with primary host plants.

Evolution of increased Medicaco polymorpha size during invasion does not result in increased competitive ability.

Species invading new habitats experience novel selection pressures that can lead to rapid evolution, which may contribute to invasion success and/or increased impact on native community members. Many studies have hypothesized that plants in the introduced range will be larger than those in the native range, leading to increases in competitive ability. There is mixed support for evolution of larger sizes in the introduced range, but few studies have explicitly tested whether evolutionary changes result in decreased competitive responses or increased competitive effects on other species in the community. Here, we show that introduced Medicago polymorpha genotypes produced 14% more aboveground and 41% more belowground biomass than genotypes from the native range, suggesting that evolutionary changes in size occurred after introduction. However, these size differences were only observed in the absence of competition. The competitive effects of introduced and native range genotypes on three species that commonly co-occur with Medicago in invaded regions were remarkably similar. These results suggest that evolutionary increases in size during biological invasions do not necessarily alter the competitive effects of the invader on other community members, but may increase invasion success in disturbed or low competition environments.

Periodical cicadas disrupt trophic dynamics through community-level shifts in avian foraging.

Once every 13 or 17 years within eastern North American deciduous forests, billions of periodical cicadas concurrently emerge from the soil and briefly satiate a diverse array of naive consumers, offering a rare opportunity to assess the cascading impacts of an ecosystem-wide resource pulse on a complex food web. We quantified the effects of the 2021 Brood X emergence and report that more than 80 bird species opportunistically switched their foraging to include cicadas, releasing herbivorous insects from predation and essentially doubling both caterpillar densities and accumulated herbivory levels on host oak trees. These short-lived but massive emergence events help us to understand how resource pulses can rewire interaction webs and disrupt energy flows in ecosystems, with potentially long-lasting effects.