The effect of epiphytic algae on the growth and production of Potamogeton perfoliatus L. in two light conditions

Direct evidence of epiphytic algal effects on the growth and production of freshwater submerged macrophytes is scarce. To obtain more reliable, quantitative data about this phenomenon, a laboratory experiment was carried out over 84 days in controlled conditions with the submerged macrophyte, Potamogeton perfoliatus. It was based on a 2x2 factorial design with two epiphytic conditions (with epiphytic algae and without) and two light conditions (high and low). Growth and production was investigated by measuring biomass, chlorophyll a concentration of leaves and net photosynthesis of the plants on Days 14, 28, 42, 70 and 84. The chlorophyll a concentration of epiphytic algae was also measured on these days. Morphological parameters of the plants were measured on Days 14, 30, 70 and 84. The chlorophyll a concentration of epiphytic algae increased significantly over the experimental period in both HLE (high light with epiphytic algae) and LLE (low light with epiphytic algae) treatments. Plants showed significant morphological changes in total shoot length, number of newly recruited shoots and expansion or contraction of the leaf surface area due to the epiphytic algal load and low light condition. The biomass (both above and below ground) and net photosynthesis rate was higher in high light than in the low light condition, but the chlorophyll a concentration was always higher in the low light condition than in the high light condition. In the plants without epiphytic algae, the chlorophyll a concentration, above ground biomass accumulation and net photosynthesis was significantly higher than in plants with epiphytic algae in both light conditions. The dead leaf dry matter was greater in the plants with epiphytic algae than in those without epiphytic algae in both light conditions. Therefore, epiphytic algae and low light phenomena both reduce growth and production. In general, plants tend to optimize low light-created shade by changing their physiology and morphology, but they could not respond to the same when epiphytic algae-created shade occurred on the leaf surface in the present experiment.