Shading effects on periphytic algal community under relaxation of nutrient limitation in a shallow lake mesocosm experiment

Periphyton is an important primary producer in aquatic ecosystems; however, the growth of its algal community can be hindered by anthropogenic factors, such as increased shading levels. Our experimental study simulated three levels of shading to evaluate the responses of periphytic algal community structure under conditions of relaxed nutrient limitation. Light availability was manipulated using shading meshes that reduced incident light by 25%, 50%, and 75%. Periphyton colonized artificial substrates, and periphyton and water samples were collected weekly. Our results demonstrate that the periphytic algal community responded to shading levels (25%, 50%, and 75%) under relaxed nutrient limitation, with reductions in algal density, biovolume, and diversity. Our findings indicate a directional shift in species composition, physiognomy, and successional trajectories toward taxa adapted to different shading levels. Changes in the community were evident from 25% shading, suggesting that light can become a determining factor and potentially limiting for algal growth under relaxed nutrient conditions. Our results suggest that variation in shading intensity reshapes both the successional dynamics and physiognomy of the periphytic algal community. Increasing anthropogenic impacts that intensify shading may affect the ecological functions of periphyton in shallow lakes, including in tropical systems, as simulated in this experimental study.