Biotic modulators of global change effects on plant communities

Understanding and predicting future plant biodiversity and productivity is critical for prioritizing global change mitigation, conservation, and restoration efforts. One major challenge is that we know remarkably little about how interspecific interactions may modulate the effects of global change factors on diversity and productivity. Here, we develop and test a synthetic conceptual framework about how different 'biotic modulators' (herbivory, plant-plant interactions, pathogens, mycorrhiza) can either amplify or mitigate the effects of global change drivers (nutrient and CO₂ enrichment, changes in rainfall and temperature) on plant community biomass and diversity. We report that herbivores mitigated both biomass increases and diversity decline caused by different global change drivers, while plant competition did not significantly alter global change impacts due to mixed effects (both amplification and mitigation). Pathogens tended to function similarly to herbivores, while mycorrhiza both amplified and mitigated community responses. Our conceptual framework further identifies mechanisms by which species interactions can modify global change effects, provides new testable hypotheses, and identifies research gaps and future research directions. We conclude that plant consumers can be important agents for stabilizing plant productivity and safeguarding plant biodiversity in the Anthropocene, but that more research is urgently needed to understand the role of other biotic modulators.