Useful information

Why are junipers burning?

The problem of spring burn is relevant not only for junipers, but also for many living creatures that unexpectedly find themselves under the influence of intense sunlight. Who of the summer residents did not happen to "burn" while working in the spring on the site: after all, during the winter the skin "weaned" from exposure to ultraviolet rays, the protective pigments accumulated in the previous spring-summer season disappear in it.

Likewise, junipers: during the winter the needles "weaned" from the intense sunlight, and in the spring, when the lighting changes, a burn is possible. The mechanism of this phenomenon is directly related to photosynthesis. The main green pigment of plants - chlorophyll - is able to absorb quanta of sunlight and "convert" their energy into the energy of chemical bonds. Normally, the energy of sunlight is directed to the synthesis of sugars. However, if the flow of light is too intense, chlorophyll cannot cope with the excess energy received. Part of it is lost in the form of quanta of red light (scientists call this process fluorescence chlorophyll). This loss is completely safe for the plant. With a significant excess of light, energy from chlorophyll is transferred to oxygen, which is formed immediately in the process of photosynthesis. Oxygen, having received a portion of energy, becomes extremely active, various strong oxidants are formed from it (for example, hydrogen peroxide). There are so many of them that the process itself is called oxidative explosion... With active oxygen, jokes are bad (remember the behavior of hydrogen peroxide in everyday life): plant cells can lose pigments and collapse. This is the mechanism of death of needles during photo fading of junipers.

With constant lighting, plants have time to get used to a certain flux of quanta. To neutralize active oxygen, cells accumulate various antioxidants: ascorbic acid (vitamin C), carotenoids (provitamin A), enzymes that destroy hydrogen peroxide and other reactive oxygen species. Misfortune occurs when the flow of light increases sharply, and the plant does not have time to synthesize protective substances. Most often this happens when the weather changes: after a long cloudy winter or spring, clear days suddenly come. It is this difference that contributes to the "burnout" of junipers and other conifers.

There is an opinion that junipers are burned in February-March, however, cases of burning needles have been recorded in mid-May, when cloudy weather did not give way to the sun for a long time. In theory, the same could happen in the summer.

The problem of burning exists not only in conifers, but also in unhardened seedlings, which are suddenly transferred to the street. The leaves are not used to the new level of illumination, there are not enough protective compounds, an oxidative explosion occurs, and whitish burn spots appear on the plants. If for most deciduous leaves renewal is a relatively easy task, for junipers, which have slow growth (like other conifers), the restoration of needles on individual branches can be difficult. The crown is exposed and the shoots die.

How does temperature affect the spring burn? In a plant, the dependence of various chemical processes on temperature varies. So, chlorophyll continues to absorb light at low negative temperatures, but the movement of molecules is slowed down, so chlorophyll cannot transfer energy to other substances and loses it through fluorescence, which is harmless. Thus, in severe frosts, light damage to the juniper is not terrible.

Temperatures close to zero are another matter: chemical transformations in plants are weak, new protective substances are not synthesized, and a small oxygen molecule is already mobile enough to take energy from chlorophyll and cause an oxidative explosion. The February and March thaws are especially dangerous in clear weather or the spring sun against the background of frosts.

It would seem that high temperatures allow the plant to quickly synthesize the necessary protective substances. Here, the relative speeds of the processes begin to play an important role: if the difference in illumination is small, then the protective system will have time to work, and there will be no burn. If the change in illumination is too great, then the protective system does not have time to cope, and photodamage is possible.

Is the reflection of light from snow harmful? The clear snow cover reflects quite a lot of sunlight. The most "ferocious" among fishermen is the March tan, which occurs not only due to the direct action of the sun, but also due to the reflected sun glare. If a lot of reflected light falls on the juniper, especially at low positive temperatures, the lower branches that were under the snow may suffer. This factor can be neutralized by scattering peat chips over the snow: this measure will speed up its melting and weaken the reflection of light.

The sun's rays can bounce off other surfaces as well: pond mirrors, metal roofs, and even white building walls. All of these factors increase the illumination and increase the risk of junipers "burning". Therefore, when planting sensitive conifers, strive to choose a place where there will be less sun glare in the spring.

Do junipers have enough light in winter? Gardeners sometimes worry about the creeping forms of junipers: in winter they are completely under the snow, which allows little light to pass through. During the winter months, plants are dormant, their respiration and growth are practically stopped, which means there is no need to replenish nutrient reserves through photosynthesis. At low temperatures, plants withstand such influences that they would never have endured in a state of active growth. So, cacti can be left in the refrigerator for the winter without lighting and watering. Bearded irises, rotting when waterlogged in summer, do not suffer from flooding with melt water at temperatures no higher than plus 70C.

What measures can be taken to protect junipers from burnout? To avoid the frustrations associated with photodamage to junipers, you need to think about the landing site from the very beginning. A sliding shadow is desirable, which will fall on the plants in the middle of the day, or pick up an area open to sunlight in the morning or evening. If this is not possible, various shading materials are used. On the south side or above the plant, you can install a protective awning or shield. Here, the old section from the picket fence, non-woven material (lutrasil, agryl, spunbond), burlap or gauze stretched over the frame will be used. Some gardeners even use a large camouflage net with “leaves” made of cloth, and a regular mosquito net will help. The main principle is that the material should create a diffused sliding shadow.

Junipers (especially pyramidal shapes) can also be wrapped with burlap in one layer or white nonwoven fabric, in one or more layers, depending on its density. In some cases, "wrapping" is more effective, since it also protects from mechanical damage by snow and "collapse" of the crown of columnar, high, spreading and spherical forms.

Junipers need such protection at a potentially dangerous time of the year - at the end of winter and early spring, when positive temperatures close to 00C are established. Later, the shading is removed, and the plants gradually adapt to the sun's rays.

Why do some types of junipers burn easily, while others almost never? Creeping species, which come from high altitude areas where strong insolation is common, do not suffer from burns. Junipers living in nature under the forest canopy are less resistant to direct sun. However, as large junipers age, their resistance to photodamage may increase.

But not all dwarf or creeping forms are highly resistant to sunburn. Many of them were obtained on the basis of species confined to forest biocenoses.

There are many varieties that differ from the natural species in the color of the needles due to a change in the pigment composition, which does not always benefit the plant. For example, if some form has a reduced carotenoid content (even if it is obtained from the most sun-resistant species), it will have to be grown in partial shade.

Chub V.V.,

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