Defining Guttation
Guttation is the process by which plants exude droplets of xylem sap from the tips or edges of their leaves. This phenomenon occurs when transpiration (water evaporation from leaves) is suppressed, typically during periods of high humidity or at night when stomata are closed, yet water absorption by roots continues.
How Guttation Occurs
Root pressure is the primary driving force behind guttation. When water intake by the roots is high and transpiration is low, water accumulates in the xylem, creating positive pressure. This pressure forces water out through specialized pores called hydathodes, located on the leaf margins, resulting in visible droplets.
An Example in Nature
You can often observe guttation on blades of grass, especially in the early morning. If you see small, clear droplets clinging to the tips of grass blades, and the air feels moist, it's very likely guttation, rather than dew. Strawberries and other low-growing plants also commonly exhibit this process.
Importance and Distinctions
While not as significant for overall water movement as transpiration, guttation helps alleviate excess root pressure and can sometimes transport small amounts of nutrients. It is distinct from dew, which forms from atmospheric moisture condensing on surfaces, and from transpiration, which involves water vapor loss through stomata.