Guttation is theexudation of drops ofxylem andphloemsap on the tips or edges of leaves of somevascular plants, such asgrasses, and also a number offungi. Ancient Latingutta means "a drop of fluid", whence modern botany formed the word guttation to designate that a plant exudes drops of fluid onto the outer surface of the plant, when the source of the fluid is inside the plant. Guttation happens in a variety of plant species.
At night,transpiration usually does not occur, because most plants have theirstomata closed. When there is a highsoil moisture level, water will enter plant roots, because thewater potential of the roots is lower than in the soil solution. The water will accumulate in the plant, creating a slightroot pressure. The root pressure forces some water to exude through specialleaf tip or edge structures,hydathodes or water glands, forming drops. Root pressure provides the impetus for this flow, rather thantranspirational pull. Guttation is most noticeable when transpiration is suppressed and the relative humidity is high, such as during the night.
Guttation formation in fungi is important for visual identification, but the process causing it is unknown. However, due to its association with stages of rapid growth in the life cycle of fungi, it has been hypothesised that during rapid metabolism excess water produced by respiration is exuded.[1]
Guttation fluid may contain a variety of organic and inorganic compounds, mainly sugars, and potassium.[2] On drying, a white crust remains on the leaf surface.
Girolami et al. (2009) found that guttation drops from corn plants germinated from neonicotinoid-coated seeds could contain amounts ofinsecticide consistently higher than 10 mg/L, and up to 200 mg/L for theneonicotinoidimidacloprid. Concentrations this high are near those of active ingredients applied in field sprays for pest control and sometimes even higher. It was found that when bees consume guttation drops collected from plants grown from neonicotinoid-coated seeds, they die within a few minutes.[3]
If high levels of nitrogen appear in the fluid, it is a sign offertilizer burn[citation needed].
Guttation droplets are consumed by numerous insects of different orders, and is an important and highly reliable source of essential carbohydrates and proteins. Unlike nectar, guttation droplets are present in an ecosystem during the entire growing season.[4]
