One of the major management problems faced by a plant is the allocation of resources between roots and shoots. Plants produce shoots that absorb light for photosynthesis, but efficient photosynthesis requires an equally efficient root system for gathering water and minerals from soil. A plant, however, has only a limited amount of energy that can be used for growth. Thus, plant growth requires a mechanism that effectively allocates energy for the growth of roots versus shoots. Botanists study this problem in a variety of ways, such as by determining the ratio of the weights of roots and shoots in plants living in different environments. This root:shoot ratio tells us how the environment affects the growth of the plant below- and aboveground. The root:shoot ratio is relatively large for seedlings and decreases gradually as a plant ages. What might be the selective advantage of relatively large roots for a seedling?
Decreasing the amount of minerals available to roots decreases the root:shoot ratio, as does diminishing light. This tells us that roots are affected more strongly by minerals and light than are shoots. If stressed by extreme environmental conditions, such as a drought, most plants route proportionally more energy and materials to their shoots.
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