The effect of mechanical damage and chemical factors on plant respiration

Any mechanical damage to plants — from injury during harvesting with a combine harvester to pruning in the orchard — sharply activates their respiration. Tissues begin to consume more oxygen, and the destruction of cell membranes releases enzymes and substrates that immediately react. As a result, plants begin to literally "burn" their own carbohydrate reserves, reducing the mass and quality of the harvest.

The intensity of the response directly depends on the nature of the impact:

• pressure causes a slight increase in respiration;
• bending leads to a moderate increase;
• cutting and deep wounds trigger a massive burst of respiratory activity.

For an agronomist, this means direct losses of produce during harvesting and transportation. Damaged fruits, berries, seeds, and stems quickly lose their marketability and mass. A typical example is the delay in processing harvested sugarcane, in which the sucrose content drops rapidly:

Plant respiration also responds sensitively to chemical treatments. Preparations that block the electron transport chain at various stages reduce the intensity of respiration. The action of the main chemical agents is distributed as follows:

• fluoride inhibits the conversion of phosphoglyceric acid to phosphoenolpyruvic acid;
• fluoroacetate and malonate block specific stages of the Krebs cycle;
• antimycin A stops electron transfer between cytochromes b and c;
• cyanide, azide, and carbon dioxide suppress the final stage of electron transport.

How plant age and carbohydrate reserves affect respiratory intensity

The intensity of respiration follows the law of mass action: the more oxidizable substrate (sugars) accumulated in the tissues, the more active the process. This is clearly visible during fruit ripening, when starch is converted into sugar. A similar process occurs in the sapwood — the young, physiologically active layers of wood under the bark, where a high concentration of carbohydrates supports intensive gas exchange.

During the growing season, the respiration of the entire plant initially increases, peaking during the period of maximum growth, and then declines (the so-called grand curve of respiration). However, if the respiratory intensity is calculated per unit of dry mass, the indicator will decrease continuously from the very beginning of the plant's life. This is because inert lignin and cellulose accumulate in the tissues, the volume of vacuoles with storage substances increases, and the proportion of living, dividing cells gradually decreases.