With ongoing climate changes, this winter's temperature values should remain mild, but the possibility of short but intense waves of frost, brought by the polar vortex, capable of suddenly lowering the mercury even further cannot be ruled out. degrees below zero. Situations that could well bring gods damage to the olive tree, particularly sensitive to rapid drops in temperatures, which would not allow it to partially dehydrate the most sensitive parts, such as not yet lignified tissues or leaves, and thus lower their freezing point.
How to intervene to limit the consequences of sudden frosts and ensure sufficient defense, which allows us to prevent or attenuate or cancel its effects?
It is appropriate to state that there are difficulties in determining the relationships that link the damage from temperature drops to the biology of olive trees, because there are numerous factors that interfere, like the humidity of the atmosphere and soil, the nutritional state of the plant and the degree of lignification and hydration of the various organs.
When temperatures drop below 10°C, the roots reduce or cancel the absorption activity, chlorophyll photosynthesis stops and the system of conducting vessels, which allows the circulation of raw and processed sap, reduces its function of translocating the nutritional elements, thus the metabolism of the the whole plant.
Walking down below 3°C, functioning of cell membranes begins to become difficult because, being composed mainly of fats and proteins, they tend to harden and lose both elasticity and the ability to regulate the flow of fluids, so much so that water migrations from the inside of the cells towards the outside are possible, causing their partial or total dehydration. The olive plant cells, however, have adaptation mechanisms and are able to produce protective substances, which function as antifreeze, such as soluble sugars and proteins, which prevent the formation of ice or reduce its harmful effects.
Furthermore, they can regulate the water content in cells to avoid damage during low temperatures.
Then to consider that in the intercellular spaces, between tissue cells, used for the circulation of gases and vapours, there is greater ease of ice formation which, increasing in volume, exerts pressure on cell membranes and internal structures, and this can damage both cell membranes and other sensitive cellular components. The presence of ice inside these intercellular spaces could lead to depressions that draw liquids from inside the cells to the outside, dehydrating them.
If the frost lasts for a long time, the crystallization of all the water present in the tissues occurs progressively, until the formation of ice crystals of increasingly larger dimensions. Inside the cell, freezing water causes two types of damage, one mechanical and one chemical.
Il mechanical damage for the formation of ice crystals is caused by an alteration of the shape of the cell, which causes malformations in its structure and shape. Furthermore, ice crystals are sharp and can break cell membranes and other surrounding tissues, leading to the death of the cell itself.
Il chemical damage it is caused because the microscopic drops of water, inside the cells, when they are about to freeze tend to join together forming pure water and, in this way, exclude the mineral salts, fats and proteins with which they are in solution and these, concentrating in the remaining unfrozen water, it would cause this water to be toxic to the cell.
If you have not intervened with autumn fertilizing, especially with contributions of phosphorus and potassium, useful for the formation of solutes within the tissues in the plant, which would act as antifreezes, it is advisable to reinvigorate the plant with foliar products to try to reduce, as far as possible, any serious damage from frost and/or cooling.
In these cases it is conceivable to implement a targeted nutrition, introducing specialties capable of stimulating the formation of "more concentrated" humors in the tissues of cellular structures, using, even in the vicinity of freezing events, products rich in potassium, boron, calcium, zinc and silicon, which are valid allies for the structuring of cell walls and could take on the function of “cryoprotectants”.
To consider that Boron plays an important role in regulating coldin fact, it contributes to the formation and stability of cell walls, indirectly influencing the resistance of plants to the cold. Boron is important also in the synthesis of compounds involved in the response of plants to cold stress and its adequate presence can contribute to greater tolerance of plants to low temperatures. These products could well be conveyed with glycol, which offers protection to plants from low temperatures; it is a viscous substance, which forms a thin film over the plant tissues, protecting them even down to -4°C -5°C, it does not interfere with the physiology of the plant and has good miscibility with water.
AIPO Director
Interregional Association
Olive producers
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