Zea mays is among the few species that avoid wasting much of the energy provided by full sunlight. Most plant species have an energy wasteful process called photorespiration in which oxygen molecules actually become consumed instead of released from the plant. This not only uses up energy in the form of ATP but also actually releases CO2. This process is more intense when under high temperatures. It apparently evolved as a mechanism to protect from damage from high light intensity. Soybeans, wheat and rice are among the crop species with this photorespiration system and are designated as C3 because they feature 3-carbon rings on the way to make glucose.
Corn, sorghum and sugar cane have another way of handling high temperatures and high light intensity without potential cell damage. Unique enzymes in the chloroplasts near the vascular bundles tie up the 3-carbon rings by adding a carbon atom, thus avoiding most of the photorespiration reaction. It is significant that these C4 plants evolved this system in tropical, drier environments.
The net effect of C4 photosynthesis in corn is increase in glucose production as the light intensity increases to full sunlight, and a reduction on glucose production with cloudy weather occurs. Leaves fully exposed to sunlight have higher rates of photosynthesis than those shaded by other leaves. Individual plants may have reduced photosynthesis because of shading by adjacent plants but total photosynthesis per land area may be increased because more leaf area is exposed to sunlight. Leaf architecture and leaf width affect total leaf area of a corn plant receiving maximum light intensity.
Further discussion of C4 photosynthesis in Corn Journal can be found by entering C4 in search on this page.
About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.