Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 10/25/2012
Publication Date: 8/19/2014
Citation: Runion, G.B., Pritchard, S.G., Prior, S.A. 2014. Leaves: Elevated CO2 levels. In: Wang, Y.Z., editor. Encyclopedia of Natural Resources. New York, NY: Taylor & Francis. p. 338-342. doi: 10.1081/E-ENRL-0120049205.
Interpretive Summary: The level of carbon dioxide (CO2) in the atmosphere is rising as a result of fossil fuel burning and land use change. Leaves are where CO2 enters plants which use the carbon to produce biomass for growth. Therefore, rising atmospheric CO2 can greatly affect plants and, while these affects are usually positive, this can depend on plant type and the environment in which they are growing. Since carbon capture by leaves forms the basis of agriculture and forestry and provides humans and other organisms with the food, clothing, and shelter they need to survive it is important to understand the affects of rising CO2 at many scales from molecular and cellular to whole leaf and whole plant up to whole ecosystems. This article provides a brief summary of the effects of the increasing atmospheric CO2 on plant leaves at various scales from molecular to ecosystem.
Technical Abstract: Burning fossil fuels and land use changes such as deforestation and urbanization have led to a dramatic rise in the concentration of carbon dioxide (CO2) in the atmosphere since the onset of the Industrial Revolution. The highly dilute CO2 from the atmosphere enters plant leaves where it is concentrated and transformed into useful organic carbon compounds (food and fiber). In light of the fact that only plant leaves serve this critical function, we provide a brief summary of the effects of rising CO2 on plant leaves at scales from the molecular to the whole plant community. Within leaves of C3 plants, photosynthesis is stimulated by elevated atmospheric CO2 which generally results in increased biomass production. Elevated CO2 also increases water use efficiency in both C3 and C4 plants by inducing partial closure of stomatal guard cells which decreases transpiration. Growth in elevated CO2 increases leaf area as well as leaf thickness and can alter leaf chemistry which can affect plant water relations and interactions with pests and diseases. While increases in leaf-level photosynthesis usually translate to increased growth and yield, decreased leaf-level transpiration does not necessarily result in lower whole plant water use; larger plants from exposure to elevated CO2 often use the same or more water on a whole plant level as their ambient CO2 grown counterparts. Effects of elevated CO2 (from the molecular to the whole plant) scale up to the community or ecosystems level and ecosystem gross primary productivity is usually increased. Reduced transpiration under high CO2 can reduce cooling and lead to higher leaf or canopy temperatures. Since not all plants respond in the same manner, growth in elevated CO2 will benefit some plants to the detriment of others and plant community structure and function can be altered. Despite all we know regarding the effects of elevated CO2 on leaves, this important research should be continued.