Rising tropospheric ozone (O 3 ) and invasion of exotic plant species are two major global environmental challenges. While elevated O 3 is known to directly influence plant invasion by asymmetrically inhibiting the growth of exotic and native species, its indirect effects on invasions via biotic interactions remain poorly understood. We conducted a common‐garden experiment to test the effects of elevated O 3 and herbivory on invasion of exotic plant species. We established replicate native plant communities, each with the same composition of five native species and separately invaded them with 14 exotic plant species under factorial combinations of O 3 (ambient versus elevated) and herbivory (present versus absent). Above‐ground biomass of invasive species was significantly influenced by Herbivory × O 3 interactions, whereas native biomass and the proportional biomass of invaders responded only to herbivory. Under ambient O 3 , herbivory strongly suppressed biomass of invasive plants, but this effect largely disappeared under elevated O 3 . By contrast, herbivory consistently reduced biomass of native plant communities and lowered proportional biomass of invasive plants regardless of O 3 . Invasive species showed strong interspecific variation in biomass responses to herbivory: Datura stramonium, Lolium perenne, Medicago sativa, Senecio vulgaris, Sesbania cannabina and Trifolium repens showed strong reductions in above‐ground biomass, with S. cannabina being most severely affected. Structural equation models confirmed direct negative effects of O 3 and herbivory on invaders, with herbivory exerting the strongest suppressive influence. Our multispecies experiment supports previous evidence that elevated O 3 can hinder exotic plant growth but provides novel evidence that it can also reduce the suppressive effect of herbivores, thereby facilitating invasion under O 3 ‐polluted conditions.
Wang et al. (Sun,) studied this question.