plant growth & development
photosynthesis | respiration | transpiration | balancing act
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A balancing act
In order for a plant to grow and develop properly, it must balance photosynthesis, respiration, and transpiration. Left to their own devices, plants do a good job of managing this intricate balance. If a plant photosynthesizes at a high rate, but its respiration rate is not high enough to break down the photosynthates produced, photosynthesis will either slow down or stop. On the other hand, if respiration is much more rapid than photosynthesis, the plant won't have adequate photosynthates to produce energy for growth. Hence, growth either will slow down or stop altogether.
When stomata are open, transpiration occurs, sometimes at a very high rate. A corn plant may transpire 50 gallons of water per season, but a large tree may move 100 gallons per day! Plants have problems if they lose too much water, so stomata close during hot, dry periods when transpiration is highest. However, CO2, which is needed for photosynthesis, also enters the plant through open stomata. Thus, if stomata stay closed a long time to stop water loss, not enough CO2 will enter for photosynthesis. As a result, photosynthesis and respiration will slow down, in turn reducing plant growth.
Many herb plants produce lots of high-energy oils, which help them survive in the dry landscapes where they evolved. These oils help them survive extended periods of stomatal closure.
