Effect Of Time Of Exposure To Uv Radiation On Photosynthetic Rate Of Hygrophila Polysperma

Abstract An experimental research was conducted to investigate the effect of time of exposure to ultraviolet radiation on the photosynthetic activity of Hygrophila polysperma. The rationale behind this research is the examination of the destructive effect of increased stratospheric ozone depletion on the productivity of plants. Productivity, in this case, will be investigated in terms of Dissolved Oxygen present in the water of the container within which the plants were placed, as this changes post irradiation. The research question of the investigation is formulated as such: "How is the photosynthetic activity of an aquatic plant species (Hygrophila polysperma), as measured by the release of oxygen per unit time, affected when placed under UVA radiation for different periods of times (10 seconds, 30 seconds, 30 minutes, 60 minutes, 120 minutes, and 180 minutes)? The method followed included the placement of different aquatic plant individuals (5 individuals per irradiation duration assessed) under optimal conditions of water nutrients, light, carbon dioxide concentration and temperature and their subsequent irradiation with UVA light for a set time interval. Immediately afterwards, the dissolved oxygen concentration of the aqueous medium in which the plants were immersed was measured using a PasPort Dissolved Oxygen Sensor. The results showed an interesting trend; at 10s of irradiation the mean percentage of oxygen production showed the highest decrease. At 30 seconds, 30 minutes and 60 minutes, the mean percentage of oxygen production decrease was smaller, indicating that the plant individuals were compensating for the damaging effect of UVA radiation. However, after an irradiation time of 120 minutes and 180 minutes, the decrease of oxygen concentration was again more prominent. By carrying out a statistical t-test, the differences between irradiation times were shown to be significant, even reaching 95%.