Submitted to: Dekker Encyclopedia of Plant and Crop Science
Publication Type: Book / chapter
Publication Acceptance Date: 1/13/2003
Publication Date: 3/17/2004
Citation: Prior, S.A., Pritchard, S.G., Runion, G.B. 2004. Leaves and the Effects of Elevated Carbon Dioxide Levels. In: Goodman, R.M. (ed.). Encyclopedia of Plant and Crop Science. pp. 648-650. Marcel Dekker, Inc., New York. Interpretive Summary: Carbon dioxide is rising steadily in the Earth's atmosphere as a result of fossil fuel combustion and land use change. Plants are affected by increased atmospheric carbon dioxide, usually in a positive manner. Leaves are the first point of contact for carbon dioxide entering plants and subsequently the soil. This trapping of carbon by leaves enables the growth of plants which plays a vital role in maintaining the environment and form the base of agriculture. This article reviews what we know and do not know about the effects of elevated atmospheric carbon dioxide on plant leaves.
Technical Abstract: Since the onset of the Industrial Revolution, the burning of fossil fuel and the clearing of land has led to dramatic rises in the concentration of CO2 in the atmosphere. Leaves concentrate highly dilute CO2 from the atmosphere and transform organic carbon compounds into useful forms (food and fiber). In light of the fact that leaves, and leaves only, serve this important purpose, we provide this short overview. Crops grown under high CO2 usually exhibit increased mass due to more photosynthetic capacity and enhanced water use efficiency but, differences exist among plants. C4 plants can exhibit growth stimulation primarily due to increase water use efficiency. The C3 plant can benefit from both increased photosynthesis and water use efficiency. Enhanced photosynthesis can lead to the accumulation of non-structural carbohydrates in leaves which has been related to a decline in photosynthesis over time caused in part by source-sink imbalances. Increases in carbohydrates may repress photosynthetic gene expression. Leaf structural changes may help interpret divergent findings with regard to photosynthetic acclimation. Under high CO2, starch accumulation may change chloroplast structure and function. Both photosynthetic and assimilate transport capacity may also be altered by CO2-induced shifts in mesophyll and vascular tissue. Changes in the leaf surface could affect water relations, susceptibility to pests and diseases, and surface properties which are important in chemical protectant application. Herbicide efficacy can vary by weed species under elevated CO2 which is important for future weed management, including control of invasive species, and also raises questions about herbicide efficacy on cover crops. Although highly variable, increases in cell expansion may contribute to larger leaf size more than increased cell division. Increased expansion appears to result from greater cell wall relaxation and/or greater cell turgor. Under high CO2, plants often exhibit increased area per leaf, greater leaf thickness, more leaves per plant, and higher total leaf area per plant, but effects on leaf area index are variable. Increases in leaf thickness is often the result of altered anatomy or starch accumulation. CO2-induced increases in leaf production and changes in leaf composition can significantly affect other trophic level organisms which utilize leaf tissue as a food substrate; this could impact pest management decisions and leaf litter decomposition rates. Leaf response to elevated atmospheric CO2 will need to be further elucidated, if we are to accurately understand and predict the development and growth of crops under future environmental conditions.