Responses of phytoplankton community dynamics to reduced underwater light in spring

Air pollution and lake eutrophication have led to a reduction in incident total radiation and water transparency in many lakes, resulting in a decrease in available underwater light. This reduction in available light depends significantly on the dynamics of spring phytoplankton communities. However, the process and mechanisms behind these effects are not yet well understood. In this study, we conducted a field mesocosm experiment to observe the responses of the phytoplankton community to varying levels of light intensity (100%, 85%, and 65% photosynthetically active radiation, PAR). Our study revealed that reducing PAR resulted in an earlier peak of cyanobacterial biomass in spring, while the biomass of chlorophytes and bacillariophytes declined with decreasing light intensity. The weakening of light intensity promoted the recovery of photosynthetic activity in cyanobacteria but reduced the photosynthetic activity in chlorophytes and bacillariophytes. Additionally, the decrease in light intensity reduced the diversity of phytoplankton communities, accelerating the rate of species turnover. However, the rate of species turnover slowed down as the dominance of cyanobacteria was established in the later stages of the experiment. Therefore, the weakening of light intensity is beneficial to the early establishment of the dominance of cyanobacteria in the phytoplankton community structure, accelerating the succession process of phytoplankton community. These findings contribute to the exploration of the effects of reduced light intensity on the establishment of cyanobacterial dominance in spring, providing valuable insights for the management of lake ecosystems.