Abstract:

 Water depth (WD) and water level fluctuation (WLF) play important roles in affecting diversity and distribution of submersed macrophytes in lakes In this study， an in situ experiment was carried out on a floating platform in Lake Erhai to explore effects of various WD and WLF on submersed macrophytes Potamogeton maackianus and P malaianus， [JP2]by planting the plants in buttes and hanging the buttes at 2 m， [JP]4 m and 6 m below water surface and adjusting WD of the buttes We observed that the WD and WLF affected growth， shoot height， shoot knots and leaf number of the plants significantly， and that 35 m and 5 m were critical maximum colonizing WD of P malaianus and  P maackianus， respectively The plants had lower biomass and less leaf number and their shoots did not elongate at deeper WD than the critical WD Increasing WD (20 cm/6 d×60 d) did not affect biomass， but increased shoot height and shoot knots of the plants at the initial 2 m WD Increasing WD (20 cm/6 d×30 d) deeper than 4 m inhibited growth of P maackianus， which could not be reversed by the following decreasing WD (-10 cm/6 d×30 d)； however， decreasing WD from 4 m and then increasing WD released stressful effects of 4 m WD on the plant WLF did not affect growth of P malaianus at 4 m WD， but decreasing WD from 4 m and then increasing WD released stressful effects of 4 m WD on the plant as compared to the stable 4 m WD WD at 6 m inhibited growth of the two plant species and caused death of the plants P maackianus was more tolerated to weak light stress than P malaianus