MadSci Network: Botany |
Frances Thank you for your question. If I were to give you a one word answer to your question it would be competition.
Plants have the unique ability of producing chemical energy from the light energy of our sun through the process of photosynthesis. The light is absorbed by pigments (chlorophyll, carotenoids, etc.) contained in the cells of the plant leaves.
When a plant is grown by itself in a pot there is sufficient light for the plant to grow. However when plants are grown in crowded conditions the light required for photosynthesis, this is light in the red range, is quickly absorbed by the leaves closest to the light. The lower leaves and stems are able to sense an increase in part of the light spectrum called far-red light, by the way as humans we does not see this light.
There is a light receptor called phytochrome that is responsible for detecting the changes in light quality. As the amount far-red light increases and red light decreases the plant senses it is being shaded by other plants. In response to the perceived shade the plant begins to grow higher in an attempt to reach better light.
So by itself the plant has no need to grow tall quickly while in a close group you see the response of trying to reach for the light.
I am including a link to some more information that will help to elaborate on my answer. The link was developed by Dr. Micheal Knee. Dr. Knee is a Professor in the Horticulture and Crop Science Department at The Ohio State University.
Try the links in the MadSci Library for more information on Botany.