Physiological Mechanisms of Crops’ Mediating Defense Response under Elevated CO2

Global climate change due to increasing anthropogenic emissions is markedly affecting natural ecosystems (Kerr 2007). Rising CO₂ levels, among other factors, are thought to be responsible for climate change. The global atmospheric concentration of carbon dioxide (CO₂) has increased from 280 μmol mol⁻¹ during the pre-industrial period to 388.5 μmol mol⁻¹ in 2010 (Dr. Pieter Tans, NOAA/ESRL, https://www.esrl.noaa.gov/gmd/ccgg/trends/) and is projected to increase to 700 μmol mol⁻¹ by the end of the twenty-first century (Aranjuelo et al. 2011). Additionally, the rise in CO₂ is often projected to increase the production and quality of agroecosystems, particularly in C3 crops (Dion et al. 2013; Uprety, 1998). Many studies have investigated the likely impacts of rising CO₂ concentration on crop growth and production (Aranjuelo et al. 2013; Leakey et al. 2006; Soares et al. 2008; Tubiello et al. 2000), and there has been general agreement on the beneficial effects of elevated CO₂ on yield, probably due to increased photosynthesis, C:N ratio, and water use efficiency from the CO₂ “fertilization effect” (Ainsworth and Long 2005; Drake et al. 1997; Slattery et al. 2013). However, yield-limiting factors such as pathogens have been ignored in most of those studies (Juroszek and von Tiedemann 2013; Pangga et al. 2011). Plants consistently face challenges from a wide array of pathogens, including fungal, bacterial, and viral attacks (Singh et al. 2000). Furthermore, disease symptoms are influenced by three main components: (i) host, (ii) pathogen, and (iii) environmental conditions (McElrone et al. 2005). Thus, the altered environmental conditions associated with elevated CO₂ will potentially modify plant disease susceptibility. However, knowledge of the effects of climate change on diseases and related plant responses is still lacking. Pathogens reduce plant productivity worldwide, and billions of dollars in plant yield are lost to 60diseases each year. Therefore, more work is needed to elucidate how plant diseases will respond to the interacting factors of elevated CO₂ climatic conditions (McElrone et al. 2010; Runion et al. 2010). Understanding such relationships is essential for predicting disease pressure and managing agricultural and natural ecosystems under changing climatic conditions.