Exudation (Latin exsudare, German 'ausschwitzen, abfließen', English exudation), occasionally also root exudation, in plant physiology refers in some cases to the excretion of substances from a plant; the material given off is called exudate. The term is not common for all excretion and secretion processes.

In ecology in particular, the term exudation is used for the diffusive excretion of monosaccharides, amino acids and other small-molecule organic compounds. Phytoplankton organisms exude up to half of the photosynthetically formed compounds and thus influence the water surrounding them. In higher plants, the release of such substances into the environment takes place via the roots, making them part of the rhizodeposition. They develop various effects in the rhizosphere, so they can affect neighbouring plants allelopathically, be used by microorganisms, etc.

In addition, gums or kino that emerge from injuries to the bark and other parts of the plant are also called exudates.

Plant roots excrete a myriad of substances present in the plant, depending on their nature and concentration, the plant species, the age and the developmental and nutritional state of the plant, as well as the soil and environmental conditions: various sugars, amino acids, organic acids, proteins, growth substances, growth inhibitors and others. The exudates serve as food for the microfauna living in the rhizosphere, and the plants benefit in symbiosis from the excretions of these animals, microbes and bacteria, for example from the nitrogen-fixing nodule bacteria.

The following were found in exudates: all 20 amino acids, 21 organic acids and inorganic acids, 15 lignin components, 11 sugars, 6 allomones (messenger substances), 5 glucosinolates, 4 fatty acids as well as various phenols and mucilages, proteins and enzymes. The root hairs secrete the enzyme phytase, which converts phosphorus-phytate complexes into easily soluble inorganic phosphorus compounds.