Plant Roots: Function and Structure

Plant Roots: Function and Structure

Plant roots aren’t just for holding the plant in the ground. They provide so much more to the plant. Did you know they communicate with other plants, fungi, and bacteria? In this article, we explore the plant’s intricate underground structure and function.

Types of Root Systems

Taproot System

The taproot system consists of one primary root, the taproot, that is large and penetrates into the soil. The taproot retrieves water, nutrients, and minerals deep within the ground. It also stores sugars or food for the plant’s survival during times of stress. The taproot has secondary roots that grow from the sides.

Because taproots extend into the ground and the secondary roots reach horizontally, these root systems take up more surface area underground. More surface area results in a stronger root system than fibrous roots.

Fibrous Root System

The primary root of the fibrous root system is the root that emerges first from the seed. After that, other roots of similar size create a network of roots. Fibrous roots stay close to the surface of the ground and do not store food like the taproot system. They are thin and hair-like.

Root Structure

Epidermis

The epidermis of the root protects the internal structures. It also aids in the absorption of nutrients and water.

Root Hairs

The root hairs take up water and nutrients from the soil. They increase the surface area where the roots reach.

Ground Tissue

Most of the inside of a root consists of ground tissue. In the root, the ground tissue’s primary function is food storage.

Waxy Layer

The waxy layer borders the root’s vascular tissue (xylem and phloem). This layer acts as a protection against unwanted substances absorbed by the root. Recent studies reveal a plant increases or decreases this layer based on its nutrient needs.

Xylem and Phloem

The xylem and phloem make up the vascular (vein) tissue in the root. The xylem transports the nutrients and water absorbed by the root to the rest of the plant. The phloem brings the sugars and other nutrients from the leaves to the roots.

Primary and Secondary Meristem

The primary meristem sits at the base of the root. It is responsible for the extension of the root system. The secondary meristem sits inside the root structure, as illustrated in the cross-section of the root. It is responsible for the root’s girth and thickness.

Root Cap

The root cap protects the growing meristem, senses gravity, and produces a lubricant that aids in the movement through the soil.

Rhizosphere and Plant Roots

The rhizosphere is a small portion (2-80mm) of soil surrounding the root system. In this soil section, roots and microbes create a reciprocal relationship.

Roots secrete substances into the rhizosphere, the soil around them. These secretions are called root exudates.

The secretions from the roots are a means of communicating with microbes, fungi, and bacteria. The secretions change depending on what microorganisms are present in the rhizosphere. With these secretions changes, the plant affects which microbes make up the soil. Vice versa, the present microbes affect which secretions come from the roots.

Adventitious Roots

Adventitious roots develop on other parts of the plants besides the roots. They may form from the stem, branch, or leaves. Some adventitious roots form through normal development, whereas others form because of stress.

Types of Adventitious Roots

Adventitious roots are divided into three categories, storage, support, and other special functions.

Storage Roots

Tuberous Roots

Tuberous roots are large and fleshy and store food for the plant. Do not get a tuberous root confused with a true tuber, a modified stem. Potatoes are true tubers, but sweet potatoes are tuberous roots.

Fasciculated Fleshy Roots

The definition of fasciculated is an arrangement in bundles. Fasciculated fleshy roots are fleshy roots that grow in a cluster, such as a dahlia.

Palmate Roots

Palmate roots resemble the palm of the hand. They are also fleshy roots.

Nodulose Roots

The fleshy part of nodulose roots occurs in the root tips. Turmeric is an example of a plant with nodulose roots.

Moniliform or Beaded Roots

As the name suggests, these roots are swollen and then constricted, creating the look of a string of beads. Some grasses, bitter gourd, and Indian spinach are examples of plants with moniliform roots.

Annulated Roots

Annulated roots look like fleshy rings attached together. Ipecac is a plant with annulated roots.

Support Roots

Prop Roots

These roots grow from the branches of specific trees. They look like aerial roots at first but then grow down into the ground, providing extra support. These prop roots resemble pillars.

Stilt Roots

Stilt roots form from the lowest node on the stem. These roots develop in a diagonal direction toward the ground. Once they are underground, they form fibrous roots. Not only do these roots add support to the plant, but they also help in the absorption of water and nutrients.

Climbing Roots

Some plants produce aerial roots from their stems that then curl and grasp a support. These roots allow the plants to get their leaves closer to the sunlight.

Floating Roots

Floating roots occur in aquatic plants. These roots act as a floatation device. They are air-filled and keep the plant afloat. These roots are sometimes referred to as respiratory roots because they aid in exchanging gases.

Contractile Roots

Contractile roots form on a bulb or corm. The name comes from their ability to push and pull the bulb or corm to the appropriate depth in the soil.

Buttress Roots

Buttress roots grow in specific large trees. They develop at the base of the stem and extend along the soil’s surface. They improve the stability of the tree.

Clinging Roots

Clinging roots are similar to climbing roots. Their main purpose is to help the plant get closer to sunlight.

Special Functions

Reproductive Roots

Reproductive roots make the propagation of the plants via the roots possible. These roots have buds that form new plants. Sweet potatoes and dahlias produce new plants with reproductive roots.

Saprophytic or Mycorrhizal Roots

Saprophytic roots create a relationship with fungi. The fungi provide water and nutrients to the plant. In return, the roots provide food for the fungi. The fungi grow either inside the root or on the root’s surface.

Assimilatory Roots

Assimilatory roots help the plant with photosynthesis. These roots contain chlorophyll and produce food for the plant.

Parasitic Roots

Plants with parasitic roots penetrate other plants to obtain water, nutrients, and minerals. They may invade the stems or roots. Mistletoe is a famous plant with parasitic roots.

Epiphytic Roots

Plants with epiphytic roots grow on other plants. Their roots hang in the air, giving them the name air plants. These roots take in the moisture from the air.

Root Thorns

Just as stems form thorns, roots do as well. These thorns defend the plant against animals. They prevent the plant from being uprooted.

Taproot Modifications

Taproot modifications are based on their shapes.

Conical Roots

Conical roots are in the shape of a cone, broad a the top and narrow at the tip.

Fusiform Roots

These roots are larger in the middle and then narrow out at the tops and bottoms.

Napiform Roots

Napiform roots are circular and fleshy at the top and then tapers off quickly to the tip.

Tuberous Roots

Tuberous roots don’t have a specific shape. They are generally large and fleshy.

As you can see from all the information provided, roots do a lot more than just provide support for the plant. They are an integral part of creating a healthy plant.

Other Related Articles

• Plant Stem
• Plant Leaves
• Parts of a Plant

Plant Roots: Function and Structure