Submitted to: Oecologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 11, 2003
Publication Date: June 1, 2004
Citation: Bunce, J.A. 2004. Carbon dioxide effects on stomatal responses to the environment and water use by crops under field conditions. Oecologia. 140:1-10. Interpretive Summary: Reductions in the aperture of pores on leaves in response to increasing concentrations of carbon dioxide in the atmosphere could reduce water use by vegetation and also potentially alter climate. Models of the global water cycle require information on how much pore apertures respond to carbon dioxide. This paper supplements and summarizes existing field-based information on this aspect of crop responses to carbon dioxide. The relative reduction in aperture varies greatly among species and varies in a complex fashion with other environmental factors. This work makes this information available for use by climate modelers in predicting effects of rising atmospheric carbon dioxide on climate and the global water cycle.
Technical Abstract: Reductions in leaf stomatal conductance with rising atmospheric carbon dioxide concentration ([CO2]) could reduce water use by vegetation and potentially alter climate. Crop plants constitute a significant fraction of the global vegetation and are major consumers of fresh water resources. Therefore crops need to be considered in forecasting effects of increased atmospheric [CO2] on the global water cycle. The largest experimental systems for exposing plants to elevated [CO2] do not include all of the feedback processes that affect responses of evapotranspiration to changes in stomatal conductance operating at larger scales. Extrapolation to larger scales can be accomplished using soil-vegetation-atmosphere models, but such models require information on how stomatal conductance responds to environmental factors as well as information on leaf area index. Considerable field-based information on this aspect of responses to elevated [CO2] now exists for most major crops, and the primary purpose of this paper is to supplement and summarize that information. The relative reduction in stomatal conductance by a given increase in [CO2] is often not constant, but varies considerably with light, temperature and humidity. Species also differ in response, with a doubling of [CO2] reducing mean midday conductances by less than 15% in some species to more than 50% in others. Elevated [CO2] increases leaf area index in some species. Simulations indicate that the relatively large reductions in stomatal conductance in crops would translate into much smaller reductions in evapotranspiration. This small projected change in evapotranspiration at elevated [CO2], which is in general agreement with limited data for naturally ventilated crops in free air carbon dioxide enrichment systems, does not preclude effects of reduced crop stomatal conductance on climate.