Elevated CO₂: a double-edged sword for plant defence against pathogens

Abstract

Human activities have caused atmospheric carbon dioxide (CO₂) concentrations to double since the onset of the industrial era, with levels continuing to rise at an unprecedented rate. This dramatic increase has far-reaching consequences for plant physiology, ecosystems, and global agriculture. While rising CO₂ may enhance plant growth through the well-known ‘CO₂ fertilisation’ effect (Ainsworth & Long, 2021), its influence on plant health is far more complex. Recent research has demonstrated that elevated CO₂ (eCO₂) can alter plant immune responses to pathogens, with highly variable outcomes. Reports indicate that eCO₂ can enhance, suppress or have no effect on plant resistance, depending on the specific host–pathogen interactions, environmental conditions, and pathogen lifestyles (Bazinet et al., 2022; Li & Ahammed, 2023; Sanchez-Lucas et al., 2023; Smith & Luna, 2023). This variability underscores the need to better understand the interplay between eCO₂ and plant immunity to predict the potential impacts of climate change on plant health. Plant diseases, caused by a wide range of pathogens, are among the most significant threats to global food security, biodiversity, and forest health. The spread and virulence of plant pathogens are already being shaped by climate change, making it critical to investigate how rising CO₂ interacts with plant defence mechanisms. The study by Bredow et al. recently published in New Phytologist (2025; doi: 10.1111/nph.20364) takes an important step towards addressing this knowledge gap. By evaluating how eCO₂ affects soybean in response to three distinct pathogen lifestyles (biotrophic, hemibiotrophic, and necrotrophic), the research provides a valuable framework for understanding the contrasting effects of eCO₂ reported in previous studies. Crucially, Bredow et al. explore the influence of eCO₂ under a concentration of 550 ppm, which reflects realistic projections for atmospheric CO₂ levels by 2050 (Hamdan et al., 2023). This approach enhances the relevance of their findings for understanding plant–pathogen dynamics in the near future, making their results directly applicable to ongoing discussions about the impacts of climate change on agriculture and ecosystems.

Understanding the broader implications of eCO₂ on plant performance remains a significant challenge due to the contrasting effects reported across diverse studies.