Growth and morphological responses of Scenedesmus obliquus to submerged macrophyte Egeria densa

Interspecific interaction are playing vital roles in shaping phytoplankton structure and affecting the food webs in freshwater ecosystems. However, the responses of green algae to allelochemically competition with submerged macrophytes were mainly focused on the growth, whereas, the algal morphology changes were usually ignored. In the present study, according to co-cultivation experimentation of submerged macrophyte Egeria densa and green alga Scenedesmus obliquus with gradient initial algal density, it was demonstrated that E. densa could allelochemically suppress the growth of S. obliquus, but the shading effects should also be considered when the algal density was low. In addition, small colonies of S. obliquus with large amount were induced in the presence of E. densa. The suppressing expression of photosynthesis-related genes LhcbM and PS II D1 might lead the reduction of cell division in S. obliquus. The small but not large colonies formation might be interpreted as the inhibitory cell division and promotion of polysaccharide by allelochemicals from E. densa. Owing to the ecological significance, much more emphasis should be placed on the morphological changes induced by interspecific competition. The results would be of great help in the prediction of phytoplankton composition and structure in freshwater ecosystems.

Automated summary

Interspecific interactions are crucial in shaping phytoplankton structure and affecting food webs in freshwater ecosystems. Previous studies on the competition between green algae and submerged macrophytes have primarily focused on growth, neglecting the changes in algal morphology. This study demonstrates that submerged macrophyte Egeria densa can allelochemically inhibit the growth of green alga Scenedesmus obliquus, with shading effects becoming important at low algal densities. Additionally, the presence of E. densa induces the formation of small colonies of S. obliquus. The suppression of photosynthesis-related genes may lead to reduced cell division in S. obliquus, and the formation of small colonies is likely a result of inhibitory cell division and promotion of polysaccharide by allelochemicals from E. densa. The findings highlight the importance of considering morphological changes induced by interspecific competition for predicting phytoplankton composition and structure in freshwater ecosystems.