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Leaf Photosynthesis: The Influence of Environmental Variables¹

ABSTRACT

A model is presented for the effects of light intensity and ambient temperature, relative humidity, and carbon dioxide concentration on leaf photosynthesis. The model treats diffusion and chemical processes occurring within the leaf, as well as the transfer of mass and energy between the leaf and its environment. Calculations have been performed for Zea mays L. (maize) which suggest the influence of environmental changes. Although leaf energy exchange processes act to moderate the effect of changes in the atmospheric temperature, a severe cooling trend may cause as much as 20% reduction in photosynthesis. Under most conditions, the rate of photosynthesis is further diminished by a reduction in relative humidity. In contrast, a 20% increase in the atmospheric CO₂ concentration, which is projected for the year 2000, will increase photosynthesis by approximately 15%. The calculations also suggest optimum ambient conditions for controlled growth environments, such as a greenhouse. In addition to a saturating light intensity of approximately 700 W/m², these conditions include a temperature and relative humidity of approximately 30C and 90%, respectively, and a CO² concentration of approximately 1,500 ppm.

Key Words: plant growth • plant environment control • climatic effects • mathematical models

¹ This work was performed while the author was a Visiting Scholar in the Dep. of Mechanical Engineering, Univ. of California, Berkeley.

² Professor of Mechanical Engineering, Purdue University, W. Lafayette, IN 47906.

Received for publication November 14, 1974.