Responses of primary producers in shallow lakes to elevated temperature: a mesocosm experiment during the growing season of Potamogeton crispus

Abstract

Climate warming may influence the relationship among macrophyte–periphyton–phytoplankton and change the producer community structure in shallow lakes, as elevated temperature has been suggested to promote the dominance of phytoplankton. We performed a 5-month experiment (starting in winter, December) to elucidate the responses of three phototrophic communities (macrophyte—Potamogeton crispus, periphyton, phytoplankton) and their interactions to elevated temperature (4.5 °C) under eutrophic, subtropical conditions. The biomass and composition of periphyton were not significantly affected by increased temperature, while the biomass of phytoplankton increased with a shift in phytoplankton composition towards higher dominance of chlorophytes and cyanobacteria. Warming also reduced the survival of P. crispus and accelerated the decline of P. crispus. At both ambient and heated temperatures, a shift occurred at the end of the experiment from a clear-state dominated by P. crispus to a clear-state dominated by filamentous algae and warming facilitated this shift. Our results thus indicated that, when submerged macrophytes diminished or disappeared, filamentous algae exhibited functional compensation that maintained low phytoplankton development, primarily at elevated temperatures.