Guttation refers to the secretion of water droplets from the pores of plants (hydathodes). It occurs due to high water pressure and low evaporation rate and helps them balance the amount of water in their system. It occurs in plants with a vascular system, such as grass, wheat, strawberry, and some fungi. However, it generally does not occur in large plants like trees because it depends on pressure, and the pressure required to force out the water is too large, which is difficult in larger plants.
Guttation occurs during the night when the soil is moist, and it is easier for the plants to absorb water. Due to excess water, the root pressure causes the water to squeeze out of the plant and move to the tip of the leaves. During the guttation process, it picks up minerals, enzymes, and other chemicals, and it is called xylem sap.
The process of Guttation occurs at night, when the stomata of plants are usually closed, due to which transpiration does not occur.
Transpiration is the process in which plants lose excess water to the environment through the stomata. It occurs in the aerial plants of plants like leaves, stems, and flowers. When the soil moisture is high, and the water potential in the roots is lower, then the water will enter the roots.
In transpiration, water gets discharged in the form of vapors, while in Guttation, it gets removed as water or xylem sap.
This will lead to the accumulation of water in plants that will create slight water pressure. This root pressure forces some water to get discharged through the leaf tip, hydathodes, or water glands in the form of water droplets. Instead of transpirational pull, root pressure provides the energy required for this upward movement.
The transpirational pull is the evaporation of water into the atmosphere from the surfaces of mesophyll cells. Due to this, a negative pressure is created on the top of the plant. This creates surface tension due to the formation of menisci in the mesophyll cell wall. And this negative tension in the xylem results in pulling out of the water from the roots and soil.
Guttation occurs through the hydathodes as the stomata are closed during the night. As it cannot function in the absence of sunlight, it is the responsibility of the hydathodes to help the plant get rid of excess water. The major difference between stomata and hydathodes is that stomata are associated with transpiration, whilst hydathodes are associated with Guttation.
Stomata, along with vapors, also facilitate the exchange of gases like oxygen and carbon dioxide. In contrast, hydathodes are only responsible for the removal of excess water and do not have any role in gaseous exchange. Stomata are present on the epidermis of leaves, small buds, and young stems. While on the contrary, hydathodes are present on the margins of leaves where the vascular supply ends. In the case of stomata, the guard cell surrounding them contains chloroplasts, while in the case of hydathodes, the surrounding cells do not contain chloroplasts.
In the case of fungi, it is hypothesized with water due to rapid metabolism the excess water produced by respiration gets exuded. In terms of chemical content, guttation fluid contains different types of organic and inorganic fluids, such as sugars and potassium. And these, after drying up, get converted to a white crust that remains on the leaf's surface.
Guttation is often confused with dew. However, dew is just the condensed moisture formed on the surface of leaves and is pure water, whereas Guttation is an endogenous process in plants in which moisture is secreted from the leaves and contains xylem sap.
Guttation is considered to be a harmful process in many places, which is not. Guttation is a completely harmless and natural process. On the contrary, it might be harmful to the plant if Guttation does not occur, as it may lead to the formation of layers of sugar and salt on the leaf's surface. These remain as small white spots and may affect the beauty of the ornamental side of the plant. Another aftereffect could be the formation of mold on the surface of leaves due to moisture. The growth of mold is supported in humid conditions. Guttation has a positive effect on the growth of some plants like strawberries. This is because it makes sure that the calcium reaches the top of the plant through the proper internal flow of water.
However, Guttation can turn out to be harmful if the plants are being over-fertilized. In that case, the minerals from the fertilizers can burn the tip of the leaves.