Root pressure is a force or the hydrostatic pressure generated in the roots that help in driving the fluids and other ions from the soil in upwards directions into the plant’s vascular tissue – Xylem.  This process is produced by osmotic pressure in the cells of the root. Root pressure is more common during the spring seasons before the leaves develop and the rate of the transpiration is rapid.

The effects of root pressure can be seen only during nights and in the early morning as the rate of evaporation is very low. The main contribution of the root pressure is to establish the continuous movements of the water molecules in the xylem which can be affected by the transpiration.

During root pressure, water passes through the root tissues freely, but the minerals do not (the root is a semi-permeable barrier). As per the natural phenomenon of osmosis,  the water molecules naturally flows from the area of low mineral concentration to the area of high mineral concentration, and this flow of water into the root pressurizes it. This is the process of osmosis is very common in all other animal and plant cell.

For example, in non-woody plants, osmosis allows plant cells to accumulate water and be plump enough to keep the plant upright.

Root pressure can be easily observed when the trees are chopped down during the spring season. When a particular tree is chopped or saw down, we can generally see a stump that bleeds sap. From this observation, it is easy to conclude that here is the explanation for sap flow in maple, sap rising to the top of tall trees, and sap movement comes from a “pump” in the roots. The sap bleeding from stumps and other wounds in some tree species is the result of root pressure, a phenomenon that occurs only under limited circumstances at certain times of the year.

Root Pressure in Plants

Root pressure is the pressure exerted by the roots of a plant on the water in the xylem vessels, which causes the movement of water upwards in the stem. It is responsible for two important processes in plants - guttation and bleeding.

Guttation

Guttation is the process of exudation of water droplets from the tips of leaves of certain plants. This process occurs when the rate of water absorption by the roots exceeds the rate of transpiration. Root pressure plays a crucial role in guttation as it causes the excess water to be pushed out of the leaf tips.

Bleeding

Bleeding is the process of exudation of sap from the cut surfaces of a plant. It occurs when the stem or bark of a plant is damaged or injured. Root pressure is responsible for the flow of sap from the cut surface as it creates a pressure gradient in the xylem vessels, which causes the sap to move out.

Root Pressure and Transpiration

Root pressure is not responsible for transpiration as it is the process of loss of water from the leaves of a plant due to evaporation. Transpiration occurs due to the difference in water potential between the leaf and the atmosphere, and it is driven by the process of diffusion.

Conclusion

Root pressure is a crucial process in plants that helps in the movement of water from the roots to the aerial parts. It is responsible for guttation and bleeding, but not transpiration. Understanding the mechanisms of root pressure can help in improving plant growth and development.