Plant-plant indirect interactions and fitness-related responses are influenced by competition and insect herbivory

Competition and herbivory are factors that usually have a negative effect on plant growth and reproduction. Responses of plants to these factors are influenced by their genetic differences in chemical profiles, resource availability and ecological interactions in a particular habitat. Phenotypic plasticity can allow plants to modify allocation to growth and other functions to optimize fitness under different environmental contexts. In a previous study, Shimola and Bidart (2019) found that plant-plant indirect interactions were dependent upon the genetic identity and presence of herbivores in emitter plants. The current study explored the relationship between emitter-receiver plant genetic similarity and presence of herbivory including intraspecific plant competition. Receiver plants of the same genotype were exposed to intact or herbivore damaged emitter plants with either the same or different genotype while grown singly or with a neighbor of the same genotype. Plant-fitness related traits of receiver plants were measured at senescence. Growth and reproductive-related traits were influenced by emitter plant treatment (genotype and herbivory level). Competition reduced the size of receiver plants (and total fruit number), but not the allocation to above- versus below-ground biomass. There was a significant herbivory by competition interaction for total fruit production per pot. Total fruit per pot was highest in receiver plants exposed to emitter plants that were undamaged and grown in competition. These results show the complexity of multiple environmental factors influencing plant-plant interactions.