LIGHT FOR COLORED CACTI
by Nicolay Shemorakov
(translated from English by Irina Okounkova)
Light is necessary for photosynthesis both for green and colored cacti. In the course of photosynthesis pigments situated in chloroplasts absorb light. The more intensive the process of photosynthesis in the stem cells is the faster the cells propagate and the stem grows.
In autotrophic plants where cacti belong a decrease of pigments in chloroplasts leads to a decrease of intensity of photosynthesis.
Research carried out by I.M.Skoulkin and E.P.Artemyeva showed that the colored forms of Gymnocalycium had a low content of chlorophyll with exception of the forms "Black Botan" and "Multicolor", and caratinoids content was normal for the families Cactaceae and Crassulaceae.
All the pigments of a cacti stem have two maxima when absorbing rays of the visible part of electromagnetic spectrum. Chlorophyll A has its first maximum in the red zone and the second in the violet one. Chlorophyll B has its first maximum in the red-orange zone and the second in the blue-violet one. Carotinoids (carotenes and xanthophylls) have one maximum of absorbing in the light-blue zone and another in the blue zone. So the energy of red, orange, light-blue and blue rays can be used in the process of photosynthesis.
Observations proved that carotinoids participate in photosynthesis together with green pigments. It was found that in the red part of the spectrum almost all the energy is absorbed by chlorophylls and in the blue part by carotinoids (S.I.Lebedev, 1988). Carotinoids can pass absorbed energy to chlorophylls. Taking into consideration all the above mentioned I suppose that for successful growing of most forms the light-blue, blue and violet rays should prevail over the red and orange. That is why in summer it would be better to defend colored forms with special filters – colored glass or plastic. You may coat window glass, especially if the room looks south, with the solution of any blue dye, for instance, methylene-blue or gouache or water-color. This way a layer of color will absorb the most part of orange, red and yellow rays. Such a filter will defend the plants from overheating in hot summer days which is important to prevent them from the summer stagnation.
In winter period colored cacti should be lighted with luminous (daylight) lamps. Such lamps give more blue, light-blue and violet rays than red and orange.
Gymnocalycium "Multicolor" and "Black Botan" should be kept at daylight in summer and under white lamps in winter because these colored forms have more chlorophylls than carotinoids.
For Eriocactus magnificus "Aurea" and Gymnocalycium "Рink" (f. pottii) use warm white lamps in winter. These cultivars contain 5 times more chlorophylls than carotinoids, consequently, in summer you'd better keep such plants behind pink filter. You can make the filter as described above.
Remark: In according to information from Michael Dubinovsky (USA) lamps from the russian manufacturers correspond to the following types of lamps: LD - cool dayligh (D, /54), LB - cool white (CW, /33), LTB - warm white (WW, /29).