Carrots

Carrots: Specialized Root Systems

The edible part of the carrot is the root system. Root systems that consist mainly of a single large root are said to have a "tap root"; in contrast, those root systems that have many branches of similar size are said to have "fibrous roots". Plants such as carrot that have a single large tap root use this large underground structure for nutrient storage.

Carrot

Despite its prominent root, the carrot has a very short, inconspicuous stem. You can see little of the carrot shoot system except the leaves that project from the tiny stem.

Let's consider the large root and small stems we find on carrots in the grocery store in terms of the changes that occur in the life of a carrot plant. When carrots are grown from seed, the seedlings form both root and shoot systems as we would expect. The leaves of the shoot system grow quickly and use sunlight to make sugars through the process of photosynthesis. Much of this sugar is transported to the root, where it is stored. The accumulation of sugar in the root causes it to expand greatly, forming the tap root we find in grocery stores. Carrots in natural environments rather than gardens live for more than one year. At the end of their first year of growth, the leaves die and the tiny stem becomes dormant. Next year, in the spring, the sugars in the root are moved upward into the stem, which begins to grow. The stem extends upward and, ultimately, forms flowers and fruits. Flowering and fruiting often requires tremendous energy, and carrots store sugars in their roots during the first year of growth to make them readily available to be broken-down for energy when the flowers and fruits expand during the second year.

Carrot stem

In our gardens, we harvest carrots as a crop after their first year of growth in order to obtain the storage roots that are filled with nutrients. If left in the ground until the second year of growth, we would find shriveled roots from which all the nutrients had been extracted.

Carrots show how parts of both the root and shoot system can modified. They have a large tap root that functions as a storage structure and a highly reduced stem that consists of little more than photosynthetic leaves, at least during their first year of growth.

Carrots also provide an example of a strategy that plants have for resource storage and use. Carrots are biennials (each lives for two years) that make sugars and store them during their first year of growth and then use them during the second year for reproduction. Alternative strategies are used by other plants.