Herbivory and elevated levels of CO₂ and nutrients separately, rather than synergistically, impacted biomass production and allocation in invasive and native plant species

Abstract

Large parts of the Earth are experiencing environmental change caused by alien plant invasions, rising atmospheric concentration of carbon dioxide (CO2), and nutrient enrichments. Elevated CO2 and nutrient concentrations can separately favour growth of invasive plants over that of natives but how herbivory may modulate the magnitude and direction of net responses by the two groups of plants to simultaneous CO2 and nutrient enrichments remains unknown. In line with the enemy release hypothesis, invasive plant species should reallocate metabolites from costly anti‐herbivore defences into greater growth following escape from intense herbivory in the native range. Therefore, invasive plants should have greater growth than native plants under simultaneous CO2 and nutrient enrichments in the absence of herbivory. To test this prediction, we grew nine congeneric pairs of invasive and native plant species that naturally co‐occurred in grasslands in China under two levels each of nutrient enrichment (low‐nutrient vs. high‐nutrient), herbivory (with herbivory vs. without herbivory) and under ambient (412.9 ± 0.6 ppm) and elevated (790.1 ± 6.2 ppm) levels of CO2 concentrations in open top chambers in a common garden. Elevated CO2 and nutrient enrichment separately increased total plant biomass, while herbivory reduced it regardless of the plant invasive status. High‐nutrient treatment caused the plants to allocate a significantly lower proportion of total biomass to roots, while herbivory induced an opposite pattern. Herbivory suppressed total biomass production more strongly in native plants than invasive plants. The plants exhibited significant interspecific and intergeneric variation in their responses to the various treatment combinations. Overall, these results suggest that elevated CO2 and nutrients and herbivory may separately, rather than synergistically, impact productivity of the invasive and co‐occurring native plant species in our study system. Moreover, interspecific variation in resource‐use strategies was more important than invasive status in determining plant responses to the various treatment combinations.

Artificial night‐time lighting and nutrient enrichment synergistically favour the growth of alien ornamental plant species over co‐occurring native plants

“…This shows that some species may respond more strongly than others to simultaneous ALAN and nutrient enrichment of the habitats. Overall, the results support previous findings that interspecific genetic variation and phylogeny can influence plant species' growth responses to environmental change (Shan et al, 2023;Wooliver et al, 2017).…”

Release from aboveground enemies increases seedling survival in grasslands

“…However, our plots are representative of local early and mid succession sites (Figure S3), and other recent work suggests that enemy effects and community effects (such as nutrient limitation) act independently rather than interactively to influence plant community assembly (e.g. Heckman, 2023;Shan et al, 2023;Zhao et al, 2023), supporting our conclusion.…”