Paper Reviewed
Li, X., Sun, Z., Shao, S., Zhang, S., Ahammed, G.J., Zhang, G., Jiang, Y., Zhou, J., Xia, X., Zhou, Y., Yu, J. and Shi, K. 2015. Tomato-Pseudomonas syringae interactions under elevated CO2 concentration: the role of stomata. Journal of Experimental Botany 66: 307-316.

Writing in the Journal of Experimental Botany, Li et al. (2015) note that elevated atmospheric CO2 concentrations in agricultural and natural ecosystems are known to reduce plant stomatal openings; but they say it is unclear how this CO2-induced stomatal alteration may or may not alter foliar pathogen infections. And, therefore, in an attempt to answer this important question, they grew tomato plants, some of which they inoculated with Pseudomonas syringae tomato strain DC3000 -- which they say is virulent to tomatos -- under ambient (380 ppm) and elevated (800 ppm) atmospheric CO2 concentrations. And what did they thereby learn?

The twelve Chinese researchers report that "elevated CO2 enhanced tomato defense against P. syringae," based on scanning electron microscopy that revealed that the stomatal apertures of elevated CO2 plants were considerably smaller than those of their ambient counterparts; and this state of affairs negatively affected the behavior of P. syringae bacteria on the upper surfaces of epidermal peels. In addition, the elevated-CO2-induced decrease in stomatal conductance was accompanied by a simultaneous increase of endogenous NO content that further mediated stomatal closure, thereby implying, in the words of Li et al., that "factors other than the stomata also play a role in elevated-CO2-induced P. syringae resistance." And in light of these findings, Li et al. declare, in the concluding sentence of their paper, that "this information is important for making proper predictions with regard to disease pressure and for designing strategies to improve plant pathogen resistance."