Tap Root

The root system is a vital component of plant anatomy, performing diverse functions essential for the survival and growth of plants. It is positively geotropic, positively hydrotropic, and negatively phototropic. 

One primary function is absorbing water and minerals from the soil, facilitating the plant's hydration and nutritional needs. Additionally, roots provide crucial anchorage to plant parts, ensuring stability and preventing the plant from being easily uprooted. Some roots are specialised for storage, serving as reservoirs for reserve food materials, exemplified by plants like carrots, radishes, turnips, sweet potatoes, and asparagus. Moreover, roots contribute to synthesising Plant Growth Regulators (PGR), influencing various aspects of plant growth and development. 

1.0Tap root

A taproot is a substantial, central, and primary root from which lateral roots emerge. Characteristically, a taproot displays a relatively straight and robust structure, tapering as it extends downward into the soil. This dominant root serves as a foundational support for the plant, and it plays a crucial role in nutrient and water absorption. The lateral roots, branching off from the taproot, contribute to the plant's stability and ability to extract resources efficiently from the surrounding soil.

Taproots originate from the radicle of a seed, giving rise to the primary root. This primary root then extends into secondary roots, which, in turn, branch out to form tertiary roots. The branching pattern may continue, resulting in the formation of rootlets. The radicle eventually undergoes natural decay in many plant species after seed germination. This process leads to the transition to a fibrous root system characterised by the absence of a dominant, downward-growing root. While most trees initiate their growth with a taproot, this primary root system undergoes a transformation within one to a few years. The mature root system adopts a broad fibrous structure, featuring predominantly horizontal surface roots and only a few vertical roots that anchor the plant deeply. 

2.0Functions of Tap Root

The taproot of a plant has many functions, including-

Anchoring:The taproot anchors the plant in the ground by burrowing deep into the soil. 

Absorbing nutrients:The taproot absorbs water, nitrogen, phosphorus, and other minerals from the soil. 

Storing nutrients
The taproot stores nutrients and carbohydrates produced by the plant through photosynthesis. This allows the plant to survive during periods of drought or lack of nutrients or sunlight. 

Transporting nutrients and translocating hormones
The taproot is the main water and resource transportation system for the plant and
also help in translocating hormones in the plant. 

Nitrogen fixation
Some taproots have nodules that can convert free atmospheric nitrogen into organic compounds. 

3.0Tap Roots for Storage of Food

1. Fusiform Roots/Spindle Roots: 

These roots, thicker in the middle and tapering on both ends, serve as storage organs. Example: Radish, where the fusiform root stores carbohydrates and other essential nutrients.

2. Conical Roots: 

Thicker at the upper side and tapering at the lower side; conical roots, like those found in carrots, store significant amounts of sugars and other carbohydrates.

3. Napiform Roots: 

These roots, swollen and spherical at the upper end and tapering like a thread at the lower end, act as storage structures for water and nutrients. Turnips and sugar beets, examples of napiform roots, store sugars, providing a reserve energy source for the plant.

4. Tuberous Roots: 

With irregular shapes and fleshy texture, tuberous roots such as those in Mirabilis store large quantities of starch and water. This storage capacity helps the plant survive adverse conditions.

Tap Roots for Nitrogen Fixation

Nodules formed on branches of roots by nitrogen-fixing bacteria (Rhizobium), nodules play a crucial role in the nitrogen fixation process. The bacteria convert atmospheric nitrogen into a form usable by plants, promoting their growth and development. Examples include leguminous plants like Pea, Gram, and Bean.

Tap Roots for Respiration

In marshy/swampy areas where oxygen is scarce, some branches of taproots in plants growing in these regions develop vertically upward to reach the surface.

Pneumatophores: These specialised roots have minute pores (pneumatophores or lenticels) facilitating air entry, ensuring the plant receives sufficient oxygen for respiration. Pneumatophores are negatively geotropic, helping the plant adapt to waterlogged environments. Examples of plants with pneumatophores include Rhizophora and Heritiera, commonly found in mangrove ecosystems.