Abstract
It has been unclear which functions of submerged macrophytes contribute to the change in chlorophyll a (Chl.a) and the microalgal community. In this study, we used a submerged macrophyte, Potamogeton pusillus, and modeled four kinds of functions of the macrophyte on the basis of the surveys in mesocosms and laboratory examinations. An ecosystem model taking into consideration the functions of a submerged macrophyte was developed. The model could simulate the change in several indexes of water quality in mesocosms. Results of simulation using the developed model indicated that allelopathy had little effect in decreasing the level of Chl.a, but caused a decrease in the biomass of cyanobacteria and an increase in that of diatoms. The combination of two functions, allelopathy and the increase in the number of individual of cladoceran by the submerged macrophyte, suggested enhanced predation of microalgae by the cladoceran owing to the decrease in the biomass of cyanobacteria and the relative increase in the biomasses of diatoms and chlorophytes by allelopathy, promoting the decrease in the level of Chl.a. The allelopathy of submerged macrophytes might have direct and indirect effects on microbial communities.
