MadSci Network: Botany

Re: Why hasn't C4 Photosynthesis taken over as the dominant process?

Date: Mon Dec 7 12:17:28 1998
Posted By: Dave Williams, Science Department Chair, Valencia Community College
Area of science: Botany
ID: 908152815.Bt
Without getting into a complicated discussion of the details and differenc es between C3 and C4 photosynthesis, let me say that C4 photosynthesis is specialized for hot, dry climates. Thus, C4 photosynthesis is better under such conditions.

The problem with C3 photosynthesis is that it depends completely on open stomata (leaf pores) for its supply of carbon dioxide (CO2) for photosynthesis. When the weather gets hot and dry the stomata close to conserve water. Unfortunately, this also keeps out the CO2. Much photosynthetic efficiency is lost in C3 plants this way.

On the other hand, C4 plants have the special ability to function well whe n CO2 is low, which often occurs when stomata are closed in the daylight. Essentially, C4 plants use a chemical mechanism to scavenge CO2.

C4 photosynthesis is not necessarily better than C3, it simply makes life in hot dry environments less stressful for the plants that use it.

Your question "Why hasn't C4 Photosynthesis taken over as the dominant process?" can be answered quite simply. Perhaps it is better than C3 photosynthesis and will eventually take over but has not had enough time. Perhaps some C3 plants will never have the opportunity to adapt by incorporating C4 mechanisms (which require structurally changes in the lea f cells) and will, because of other, as yet unrecognized, advantages, remain extant for a long time. It's difficult to answer such questions except b y speculation.

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