A meta-analysis of the effects of elevated CO2 on plant-arthropod interactions highlights the importance of interacting environmental and biological variables

Background/Question/Methods

In the face of climate change, recent research has aimed to provide general conclusions about its impacts on plant-animal interactions. For the most part, we have been unable to achieve this goal due to complex interactions between environmental variables and differences in the responses between both plant and herbivore functional groups. However, summarizing the findings from all of the research in this field through meta-analyses may allow us to determine where generalizations can be made and where they should not. We first conducted a meta-analysis of 122 studies to determine the effects of elevated CO₂ alone on 20 herbivore performance variables. In a separate meta-analysis of 170 studies, we then examined the effects of interactions between CO₂ and other critical environmental factors (nitrogen availability, temperature, drought, and light availability) on plant variables important for herbivore performance, including growth and allocation, physical properties, and primary and secondary metabolites.

Results/Conclusions

In response to elevated CO₂, the meta-analysis showed decreases in herbivore relative growth rates, conversion efficiencies, pupal weight, and relative damage while relative consumption rates and development times increased. However, responses differed between orders and feeding guilds, particularly in abundance and fecundity. For plant responses, significant interactive effects of CO₂ with nitrogen availability and temperature were found. Both biomass and total non-structural carbohydrates showed a greater positive response under elevated CO₂ when nitrogen availability was high. Total phenolics increased less under elevated CO₂ when temperatures were also elevated. Differences in the direction of responses to elevated CO₂ between plant functional groups were also found, with total glycosides increasing in trees under elevated CO₂ but decreasing in herbs and forbs. There were also cases of three-way interactions, wherein one plant functional group showed a significant interaction between CO₂ and another environmental factor but the other group did not. Therefore, when predicting responses of herbivores to climate change, we need to consider all relevant environmental factors and the functional group of the host plant and of the herbivore itself.