Chemically mediated plant-enemy interactions promote positive biodiversity effects on young tree growth

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posted on 2025-04-18, 13:26 authored by Catherine FaheyCatherine Fahey, Karin BurghardtKarin Burghardt, Eric Griffin, Kimberly KomatsuKimberly Komatsu, Melissa K. McCormick, Jamie PullenJamie Pullen, Brian Sedio, John Parker

The tree diversity-productivity relationship is key to effective forest restoration and management; however, it remains unclear what role foliar chemical diversity and interactions between trees and their enemies play in driving this relationship. Trees produce chemical metabolites in their leaves that impact herbivory and pathogen infection. If trees alter the diversity of metabolites they produce when grown in more diverse communities, this could impact interactions with herbivores and pathogens. Ultimately, these tropic interactions with plant enemies, mediated by chemical diversity, could be important drivers of diversity-productivity relationships.
Using a large-scale tree diversity experiment, we used a focal tree sampling design from 14 species across a gradient of tree species richness to assess the role of foliar chemicals and trophic interactions in the diversity-productivity relationship. We used untargeted metabolomics to measure foliar phytochemical diversity, monitored tree-enemy interactions, including foliar fungal pathogens, caterpillar communities, and deer browsing, and modelled their relationship to tree growth using path analysis.
We unraveled significant evidence for top-down mediation of the diversity-productivity relationship driven primarily by herbivores rather than foliar pathogens, and contrasting effects of foliar chemical diversity on different enemy types. Individual trees growing in more diverse communities had higher phytochemical diversity and higher caterpillar richness, but lower leaf fungal pathogen richness. Leaf phytochemical diversity was positively associated with caterpillar richness and fungal pathogen richness, but negatively associated with browsing by white-tailed deer (Odocoileus virginianus). Path analysis revealed that phytochemical diversity, caterpillar richness, insect damage, and deer damage – but not foliar pathogens – all mediated positive indirect effects of tree richness on tree growth rate.
Synthesis: We highlight the significant mediation of diversity-productivity relationships via contrasting effects of phytochemical diversity on plant-enemy interactions. Ultimately, our study underscores the importance of incorporating trophic interactions into biodiversity-ecosystem function studies.