Plant growth-defense trade-offs are general across interactions with fungal, insect, and mammalian consumers.

Plants face trade-offs between allocating resources to growth, while also defending against herbivores or pathogens. Species differences along defense trade-off axes may promote coexistence and maintain diversity. However, few studies of plant communities have simultaneously compared defense trade-offs against an array of herbivores and pathogens for which defense investment may differ, and even fewer have been conducted in the complex natural communities in which these interactions unfold. We tested predictions about the role of defense trade-offs with competition and growth in diversity maintenance by tracking plant species abundance in a field experiment that removed individual consumer groups (mammals, arthropods, fungi) and added nutrients. Consistent with a growth-defense trade-off, plant species that increased in mass in response to nutrient addition also increased when consumers were removed. This growth-defense trade-off occurred for all consumer groups studied. Nutrient addition reduced plant species richness, which is consistent with trade-off theory. Removing foliar fungi increased plant diversity via increased species evenness, whereas removal of other consumer groups had little effect on diversity, counter to expectations. Thus, while growth-defense trade-offs are general across consumer groups, this trade-off observed in wild plant communities does not necessarily support plant diversity maintenance.

Seasonal shifts from plant diversity to consumer control of grassland productivity.

Plant biodiversity and consumers are important mediators of energy and carbon fluxes in grasslands, but their effects on within-season variation of plant biomass production are poorly understood. Here we measure variation in control of plant biomass by consumers and plant diversity throughout the growing season and their impact on plant biomass phenology. To do this, we analysed 5 years of biweekly biomass measures (NDVI) in an experiment manipulating plant species richness and three consumer groups (foliar fungi, soil fungi and arthropods). Positive plant diversity effects on biomass were greatest early in the growing season, whereas the foliar fungicide and insecticide treatments increased biomass most late in the season. Additionally, diverse plots and plots containing foliar fungi reached maximum biomass almost a month earlier than monocultures and plots treated with foliar fungicide, demonstrating the dynamic and interactive roles that biodiversity and consumers play in regulating biomass production through the growing season.

Conspecific leaf litter induces negative feedbacks in Asteraceae seedlings.

The plant soil feedback (PSF) framework has been instrumental in understanding the impacts of soil microbes on plant fitness and species coexistence. PSFs develop when soil microbial communities are altered due to the identity and density of a particular plant species, which can then enhance or inhibit the local survival and growth of that plant species as well as different plant species. The recent extension of the PSF framework to aboveground microbiota, termed here as plant phyllosphere feedbacks (PPFs), can also help to determine the impact of aboveground microbes on plant fitness and species interactions. However, experimental tests of PPFs during early plant growth are nascent and the prevalence of PPFs across diverse plant species remains unknown. Additionally, it is unclear whether plant host characteristics, such as functional traits or phylogenetic distance, may help to predict the strength and direction of PPFs. To test for the prevalence of litter-mediated PPFs, recently senesced plant litter from 10 native Asteraceae species spanning a range of life history strategies was used to inoculate seedlings of both conspecific and heterospecific species. We found that exposure to conspecific litter significantly reduced the growth of four species relative to exposure to heterospecific litter (i.e., significant negative PPFs), three species experienced marginally significant negative PPFs, and the PPF estimates for all 10 species were negative. However, neither plant functional traits, nor phylogenetic distance were predictive of litter feedbacks across plant species pairs, suggesting that other mechanisms or traits not measured may be driving conspecific negative PPFs. Our results indicate that negative, litter-mediated PPFs are common among native Asteraceae species and that they may have substantial impacts on plant growth and plant species interactions, particularly during early plant growth.