Plant Responses to Rising Carbon Dioxide and Potential Interactions with Air Pollutants

Abstract As global population increases and industrialization expands, carbon dioxide (CO 2 ) and toxic air pollutants can be expected to be injected into the atmosphere at increasing rates. This analysis reviews a wide range of direct plant responses to rising CO 2 , increasing levels of gaseous pollutants, and climate change, and to potential interactions among the factors. Although several environmental interactions on stomata and foliage temperatures are reviewed briefly, a comprehensive review of effects of potential climatic change on plants is not a major objective of this analysis. Research shows that elevated CO 2 increases photosynthetic rates, leaf area, biomass, and yield. Elevated CO 2 also reduces transpiration rate per unit leaf area, but not in proportion to reduction of stomatal conductance, because foliage temperature tends to rise. With increasing leaf area and foliage temperature, water use per unit land area is scarcely reduced by elevated CO 2 . Increases in photosynthetic water‐use efficiency are caused primarily by increased photosynthesis rather than reduced transpiration. Gaseous pollutants (O 3 , SO 2 , NO x , H 2 S) affect plants adversely primarily by entry through the stomata. An example calculation showed that reduction in stomatal conductance by doubled CO 2 could potentially reduce the effects of ambient O 3 and SO 2 by 15%. However, information on the interaction of CO 2 and air pollutants is scanty. More research is needed on these interactions, because regional changes in air pollutants are occurring concurrently with global changes in CO 2 .