The influence of monochromatic light with different wavelengths on the growth of aquarium plants

Abstract

The aim of our work is to determine the growth efficiency of aquarium plants under conditions of their separate monochromatic illumination (red, yellow, green and blue waves) under continuous exposure for 60 days at 20 – 22 °C.

Materials and Methods. For the study, we selected aquatic plants, living in different layers of the water column – hornwort (Ceratophyllum demersum L., 1753), echinodorus (Echinodorus quadricostatus Fasset,1955) and pistia (Pistia stratiotes L., 1753). All aquariums were wrapped in black paper to eliminate outside lighting. Over the water surface, 6 LEDs of the FYL-3014 SRC brand were fixed. These LEDs generated waves with a length of l = 660 nm (red), 590.2 nm (yellow), 574 nm (green) and 470 nm (blue). The total power of the waves of different colors was regulated using variable resistors. Irradiation of plants was carried out continuously. In the process of the research, we repeatedly measured the mass, length of leaves and plant roots.

Result. We determined that the growth of the mass, leaves, and roots of Echinodorus quadricostatus and Ceratophyllum demersum is maximum, when illuminated by blue waves (the total increase in morphometric parameters is 31% and 37%, respectively). Smaller growth of plants was noted for red waves (16% and 33%). Yellow and green waves suppressed a mild increase of their parameters by 5 – 6%. For Pistia stratiotes the maximum growth was noted primarily for the plant mass for red light waves (14%), for blue and green the parameters remained almost unchanged. The monochromatic yellow light led to the degradation of this plant. The averaged effect of the total effect of monochromatic waves in all studied parameters of various aquatic plants is estimated. According to our data, blue and red light quite effectively support the growth of all aquatic plants, when illuminating the water system with yellow and green waves, the growth of aquatic plants is minimal.

Conclusions. It was revealed, that the efficiency of light absorption by various aquatic plants is significantly different, while the main factor of such differences is their species composition, but not the depth of the plant in the water column. Such plants as Pistia stratiotes, Ceratophyllum demersum and Echinodorus quadricostatus exhibit the intensive growth under the influence of blue or red light. In this case the maximum growth of the mass, root length, linear size of leaves in 60 days reaches 30 – 35% (for different types of plants). Influence isolated green and yellow light in aquatic plants gives a slight positive growth effect (5 – 8%), or even lead to the inhibition of growth and death (Pistia stratiotes). Obviously, the monochrome illumination of aquarium systems can be used to minimize energy costs during growing industrial aquatic plants for food purposes, as well as for propagating individual decorative species. Our data show that the growing of studied aquatic plant species is most effective (energy saving, plant growth rate) under the influence of blue or red light, and possibly a combination of both. We say that the selection of aquarium plants for growing or aquarium design goals must be carried out, taking into account the specifics of their response to the selected frequency of light waves. We can recommend additional illumination of aquatic plants with green and yellow light in an aquarium only for design purposes