Plant Physiology - Musienko M. M. 2001

Physiology of Excretion in Plants
Volatile Plant Emissions

The air surrounding plants is constantly filled with various scents, saturated with aromatic gases and vapors. Everyone is familiar with the scent of blooming flowers, Swelling buds, decaying leaves, or even fertile soil and marsh mud. This is because many plants produce physiologically very active volatile emissions (Hrodzynskyi, 1983). Volatile emissions refer to various substances released by above-ground Organs that are not localized in glands, are quite diverse, and are not always identified. Various Methods are used to collect them, all based on the same principle: plants are placed in a hermetic chamber through which purified air is pumped. Qualitative analysis of volatile emissions is carried out using various chemical micro-analysis methods—such as gas and Gas-Liquid Chromatography, polarography, and mass spectrometry.

A wide range of substances of various origins has been detected in volatile emissions: hydrogen, hydrocyanic acid, Essential Oils, Hydrocarbons (isoprene, Ethylene, propylene, butylene, isobutylene), aldehydes (formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde), alcohols (methanol, ethanol, propanol), ketones, organic acids, esters, hormone-like substances, etc. The Practical significance of volatile emissions is determined by their biological activity and lies in utilizing the mutual influence (positive or negative) of plants within phytocenoses. For instance, the biological purpose of essential oil vapors is believed to be the cooling of the plant and its protection from excessive Water loss. It is quite possible that volatile emissions serve to repel insects and herbivores and exert an allelopathic effect on surrounding plants. For medicinal purposes, the phytoncide effects of volatile emissions from both cultivated and wild plant species are widely utilized.

The composition of many volatile emissions has not yet been studied, but they are very frequently toxic to humans. For example, the leaves of *Clematis* release such a quantity of volatile Alkaloids of the proto-anemonin type that leaving the plant indoors can cause severe poisoning. Gaseous emissions from walnut trees are also quite harmful. Volatile phytoncides of wormwood, hogweed, bird cherry, almond, and dozens of other plants have a detrimental effect on microorganisms, lower animals, and plants, inhibiting seed germination, Photosynthesis, and Other Functions of the plant Organism.

The few analyses conducted so far show that clay particles in ordinary soil adsorb A wide variety of volatile substances from the air: a mixture of carboxylic acids, ammonia, hydrocarbons, aldehydes, ketones, complex alcohols, essential oils, etc. Soil volatile compounds allow microorganism colonies to proliferate on clean Glass without any other nutrient source.

Aromatic substances are also produced by plant roots and swelling seeds. Many volatile compounds are formed during the decomposition of plant residues, including alcohols, aldehydes, ketones, and hydroxy acids. It is hardly surprising that every soil has its own distinct smell. Plants react strongly to the scents of the earth; adsorbed soil gases and volatile substances can be absorbed and assimilated by plants. Since these compounds are mostly physiologically active, they either stimulate or inhibit plant growth processes.

Furthermore, volatile substances in the soil affect the taste qualities of plant produce. This issue has been scarcely researched scientifically, but viticulture practice shows that soil characteristics strongly influence the "bouquet" of wine. One can grow the same grape variety under completely identical conditions, yet the resulting wine may lack the characteristic complex of flavor profiles.

Similarly, the taste of potatoes is determined not only by the content of starch or other nutrients, but also by the conditions in which the given variety was grown. In light sandy soil, which does not accumulate volatile compounds, potatoes yield a better taste than in clay soil or peat bogs. Thus, volatile emissions from plants and soil are of considerable importance for plant life and productivity, although modern science and practice still pay little heed to this. This presents a vast field of activity for future researchers and a major reserve for further increasing soil fertility.