A meta‐analytical review of the effects of elevated CO₂ on plant–arthropod interactions highlights the importance of interacting environmental and biological variables

Summary We conducted the most extensive meta‐analysis of plant and animal responses to elevated CO 2 to date. We analysed > 5000 data points extracted from 270 papers published between 1979 and 2009. We examined the changes in 19 animal response variables to the main effect of elevated CO 2 . We found strong evidence for significant variation among arthropod orders and feeding guilds, including interactions in the direction of response. We also examined the main effects of elevated CO 2 on: six plant growth and allocation responses, seven primary metabolite responses, eight secondary metabolite responses, and four physical defence responses. We examined these response variable changes under two‐way and three‐way interactions between CO 2 and: soil nitrogen, ambient temperature, drought, light availability, photosynthetic pathway, reproductive system, plant growth rate, plant growth form, tissue type, and nitrogen fixation. In general we found smaller effect sizes for many response variables than have been previously reported. We also found that many of the oft‐reported main effects of CO 2 obscure the presence of significant two‐ and three‐way interactions, which may help better explain the relationships between the response variables and elevated CO 2 . Contents Summary 321 I. Introduction 322 II. Methods 323 III. Herbivore responses to elevated CO 2 328 IV. Plant responses 329 V. Searching for general responses to elevated CO 2 332 VI. Limitations and future studies 334 Acknowledgements 335 References 335