Influence of ultraviolet radiation on aquatic plants in conditions of low lighting

The effect of ultraviolet radiation (UV-r) on aquatic vegetation in conditions of general insufficient illumination was studied in laboratory conditions. In the studies such species of aquatic vegetation were used – submerged hornwort (Ceratophyllum demersum), thai fern (Microsorium pteropus), and globular cladophore (Aegagropila linnaei). The studies were carried out simultaneously in 3 aquariums, 3 liters each, with five iterations. For each of the experiments, the containers with water were covered with black paper on all sides, and 3 plants of each species were placed. Low-power LEDs were installed above the water surface of each aquarium. 2 white LEDs of the FYL-3014SRC brand (each with a power of 0.06 W at a luminous intensity of 600 mcd) were used for control experiments. In other versions of experiments with irradiation, we used – 2 white and 2 UV-diodes (similar power), and 2 white diodes together with 6 UV-diodes. Every week during the experiment, the morphometric parameters (weight, leaf area, length) and color of vegetation were measured during a 30-day continuous exposure from the sources described above. At the end of the experiment, it was found that with a general low power of white illumination, the presence of additional UV-r can have a multidirectional effect on vegetation that lives at different levels of the water system. Thus, UV irradiation negatively affects rootless plants of the upper layers of aquatic systems (Ceratophyllum demersum), probably due to known disturbances in the their photosynthetic apparatus. UV-r led to a decrease in the mass and leaf area of such plants (by 80–90 %), a change in their color, disruption of their vital activity, the development of tissue decay processes and even death by the end of the experiment. On root plants (Microsorium pteropus) with arrow-shaped leaves pointing upwards, additional UV-r can support the light balance and to some extent compensate (by 10–15 %) the overall decline in the level of their development (by 60–75 %). Bottom vegetation (Aegagropila sauterii), living at a depth of up to 5 m, is able to fully compensate for the lack of natural illumination by UV irradiation. UV-r penetrates the water column and after re-radiation on elements of aqueous solution penentrates to a considerable depth in the form of longer waves, and then used of plants with a general increase in the measured parameters by 5–20 %. This article concludes that the final effect on aquatic plants is formed by the depth of their habitat and the total intensity of light falling on the surface of the aquatic system. At the same time, under conditions of a lack of light, UV-r can act negatively on plants that are located close to the surface of the water, and at the same time positively as an additional source of energy – on benthic plants.