Plant Physiology - Lecture Notes - O. M. Tarnopilska 2019

8. Plant adaptation and resistance to adverse environmental factors
8.7 Gas resistance

Gas resistance is the ability of plants to maintain their vital activity under METABOLISM/18.html">The Influence of harmful gases. The degree of plant gas resistance is influenced by physiographic and meteorological conditions. Plants lack an evolutionary formed adaptation system against harmful gases; therefore, their ability to withstand the NEGATIVE IMPACT OF gases relies on mechanisms of resistance to other adverse factors. This is because modern flora evolved under conditions where the concentration of harmful gases in the atmosphere (resulting from volcanic activity, fires, and chemical processes) was extremely low. Such an atmospheric composition was established about 1 billion years ago As a result of autotrophic activity. Evidently, the cleansing of Earth's primary atmosphere from ammonia, hydrogen sulfide, methane, carbon monoxide, and other substances was actively carried out by Proterozoic and Paleozoic autotrophic plants, which must have possessed gas-resistance mechanisms. However, as oxygen levels in the atmosphere increased and harmful gases decreased, these mechanisms were lost.

Atmospheric pollution associated with the expansion of human industrial activity is growing on such a catastrophic scale that the self-regulation systems of the biosphere can no longer cope with purification. Human activities (industry, motor transport, etc.) release more than 200 different components into the air. These include gaseous compounds: sulfur dioxide (SO₂), nitrogen oxides (NO, NO₂), carbon monoxide (CO), fluorine compounds and others, Hydrocarbons, acid vapors (sulfuric, sulfurous, nitric, hydrochloric), phenol, etc., as well as solid particles of soot, ash, and dust containing toxic oxides of lead, selenium, zinc, etc. In industrially developed countries, air pollution is caused by transport emissions (52.6%), heating systems (18.1%), Industrial processes (17.9%), waste incineration (1.9%), and other processes (9.5%).

Air-polluting components (exhalates) are classified according to particle size, sedimentation rate under gravity, and electromagnetic spectrum into dust, vapor, mists, and smoke.

Gases and vapors easily penetrate plant Tissues through Stomata and can directly affect cellular metabolism by entering into Chemical Reactions at the level of Cell walls and membranes. Dust, settling On the surface of a plant, clogs the stomata, thereby impairing Gas Exchange in leaves, obstructing Light absorption, and disrupting the Water regime.

According to the degree of decreasing toxic effect on plants, gases can be arranged in the following series:

F₂ > Сl₂ > SO₂ > NO > СО > СО₂ or Сl₂ > SO₂> NH₃> HCN > H₂S.

Under pollution conditions, the Respiration process initially tends to accelerate and then slows down as the extent of damage increases. All these changes disrupt Plant Growth and accelerate Aging processes. Coniferous species suffer particularly severely from acid gases.

Based on response characteristics (i.e., the speed and intensity of pathological processes caused by gases), plants are distinguished by gas sensitivity and gas resistance. An essential property of plant gas resistance is The ability to regulate the uptake of toxic gases, maintain cytoplasmic buffering capacity and ionic balance, and detoxify resulting poisons.

Plant gas resistance increases with the optimization of mineral Nutrition and seed hardening. Soaking seeds in weak solutions of hydrochloric and sulfuric acids enhances Plant resistance to acid gases. Although atmospheric pollution causes great damage to vegetation, plants themselves—apart from regulating water, wind, and other environmental regimes—constitute a powerful factor in purifying the atmosphere.