Elevated CO2 alters soybean physiology and defense responses, and has disparate effects on susceptibility to diverse microbial pathogens

O_LIIncreasing atmospheric CO2 levels have a variety of effects that can influence plant responses to microbial pathogens. However, these responses are varied, and it is challenging to predict how elevated CO2 (eCO2) will affect a particular plant-pathogen interaction. We investigated how eCO2 may influence disease development and responses to diverse pathogens in the major oilseed crop, soybean (Glycine max [L.] Merr.). C_LIO_LISoybeans grown in ambient CO2 (aCO2, 419 parts per million (ppm)) or in eCO2 (550 ppm) were challenged with bacterial, viral, fungal, and oomycete pathogens, and disease, pathogen growth, gene expression and molecular plant defense responses were quantified. C_LIO_LIIn eCO2, plants were less susceptible to Pseudomonas syringae pv. glycinea (Psg) but more susceptible to bean pod mottle virus, soybean mosaic virus, and Fusarium virguliforme. Susceptibility to Pythium sylvaticum was unchanged, although a greater loss in biomass occurred in eCO2. Reduced susceptibility to Psg was associated with enhanced defense responses. Increased susceptibility to the viruses was associated with reduced expression of antiviral defenses. C_LIO_LIThis work provides a foundation for understanding of how future eCO2 levels may impact molecular responses to pathogen challenge in soybean and demonstrates that agents infecting both shoots and roots are of potential concern in future climatic conditions. C_LI