Factors affecting Root Pressure

Take a look out your window. Even the tallest trees have gravity-defying characteristics, allowing nutrients to be ‘sucked’ up from the deepest depths of the soil and transferred to the topmost branches! Do you know how?

Plants are complex creatures, and root pressure is one of the many fascinating activities of a plant. Root pressure is the concept that a plant’s roots may sustain a higher or lower pressure depending on their environment. It does this to encourage or inhibit nutrient intake.

In other words, a plant’s root system may change its pressure in order to either: a) let water and/or nutrients rise throughout the plant, or b) push water and/or nutrients out of the plant. Biologists are often concerned with the former and how it influences the increase of water and nutrients in a plant.

What is Root Pressure?

In plants, root pressure is a force that assists in driving fluids upward into water-conducting channels (xylem). It is mostly caused by osmotic pressure in the cells of the roots and may be seen as fluid exudation when the stem is severed immediately above ground.

Although root pressure contributes to the rise of water in vascular plants, it is inadequate for the flow of sap against gravity, especially in the tallest trees. Furthermore, the fact that root pressures are lowest when water loss from leaves (transpiration) is highest, which is precisely when plants require the most water, indicates that root pressure is not driving sap flow.

The Theory of Root Pressure

• Priestley proposed this theory (1916).
• All plants actively absorb surplus water and tend to build up a positive hydrostatic pressure inside the root system, which is known as root pressure.
• The water is forced upwards along the length of the stem to a little height as a result of this activity.
• The diffusion gradient causes pressure to build up inside the xylem, which is maintained by the activity of living cells.
• As a result, root pressure contributes significantly to water transfer.

Factors Affecting Root Pressure

The following elements affect root pressure:

1. The quantity of xylem vessels in the root
2. The soil’s water potential
3. The quantity of root hairs
4. The pace at which the roots absorb water
5. The stem’s water potential
6. The rate of transpiration

External Factors Affecting Transpiration Include:

1. Temperature: As the temperature of the surroundings rises, so does the rate of transpiration. When the temperature rises, the rate of water vapour diffusion via the stomata rises, as does the rate of evaporation from the leaf surface.
2. Humidity: As the humidity of the environment increases, the rate of transpiration reduces. When the humidity is high, the rate of water vapour diffusion via the stomata is low, as is the rate of evaporation from the leaf surface.
3. Wind: As the wind speed increases, so does the rate of transpiration. When the wind speed is strong, the rate of water vapour diffusion via the stomata is high, as is the rate of evaporation from the leaf surface.
4. Soil Moisture: As soil moisture content drops, the rate of transpiration rises. When the soil moisture content is high, the rate of water vapour diffusion via the stomata is low, as is the rate of evaporation from the leaf surface.

Limitations of Root Pressure

• It is unable to move sufficient volumes of water upward to meet the water needs.
• It has little effect on the circulation of water in tall trees such as gymnosperms.
• The quantity of fluid transferred by root pressure is insufficient for quantifying water flow in the xylem of many plants.
• When the water needs are high in the summer, root pressure appears to be absent.
• It is more common at night when evapotranspiration is low.

Root Pressure (Positive and Negative)

Guttation from leaves or bleeding from severed stems are common indicators of positive pressure.

Root pressure can occur in fine roots, where soil water is the source, or in woody roots and stems, where water stored in living cells, fibres, cell walls, and living thing areas is the source.

Root pressure is defined as the positive pressure that develops inside the roots of plants as a result of the quick and continuous absorption of nutrients from the soil.

The development of root pressure is due to active absorption, which is dependent on the active buildup of materials in xylem sap.

Typically, root pressure builds throughout the night when absorption is highest and transpiration is lowest.

During the day, transpiration is at its highest. The water lost via transpiration leads the guard cells and other epidermal cells to become flaccid. They, in turn, absorb water from the xylem.

This effectively causes a negative pressure, also known as tension, within the xylem vessels, which extends from the surfaces of the leaves to the end of the roots, all the way to the stem.

Conclusion 

Although root pressure contributes to the rise of water in vascular plants, it is inadequate for the flow of sap against gravity, especially in the tallest trees. The water is forced upwards along the length of the stem to a little height as a result of this activity. When the temperature rises, the rate of water vapour diffusion via the stomata rises, as does the rate of evaporation from the leaf surface. When the humidity is high, the rate of water vapour diffusion via the stomata is low, as is the rate of evaporation from the leaf surface. The quantity of fluid transferred by root pressure is insufficient for quantifying water flow in the xylem of many plants. When the water needs are high in the summer, root pressure appears to be absent.