Elevated atmospheric carbon dioxide and plant immunity to fungal pathogens: do the risks outweigh the benefits?

Anthropogenic emissions have caused atmospheric carbon dioxide (CO(2)) concentrations to double since the industrial revolution. Although this could benefit plant growth from the ‘CO(2) fertilisation’ effect, recent studies report conflicting impacts of elevated CO(2) (eCO(2)) on plant–pathogen interactions. Fungal pathogens are the leading cause of plant disease. Since climate change has been shown to affect the distribution and virulence of these pathogens, it is important to understand how their plant hosts may also respond. This review assesses existing reports of positive, negative, and neutral effects of eCO(2) on plant immune responses to fungal pathogen infection. The interaction between eCO(2) and immunity appears specific to individual pathosystems, dependent on environmental context and driven by the interactions between plant defence mechanisms, suggesting no universal effect can be predicted for the future. This research is vital for assessing how plants may become more at risk under climate change and could help to guide biotechnological efforts to enhance resistance in vulnerable species. Despite the importance of understanding the effects of eCO(2) on plant immunity for protecting global food security, biodiversity, and forests in a changing climate, many plant–pathogen interactions are yet to be investigated. In addition, further research into the effects of eCO(2) in combination with other environmental factors associated with climate change is needed. In this review, we highlight the risks of eCO(2) to plants and point to the research required to address current unknowns.