THE PHYSIOLOGICAL EFFECTS OF SPRING LOW WATER LEVEL ON FOUR SUBMERGED MACROPHYTES

To study effects of spring low water level on physiology (such as Fv/Fm, total chlorophyll content and soluble sugar) of different submerged macrophytes, three shallow water levels (18 cm, 36 cm and 54 cm) were treated with three native submerged plants Potamogeton maackianus, Myriophyllum spicatum and P. crispus, and an alien species Elodea nuttallii. The results showed that decreasing water levels increased the Fv/Fm of P. maackianus, P. crispus and E. nuttallii but not on M. spicatum. Fv/Fm of E. nuttallii was significantly higher than that of other three native species at all water levels. The total chlorophyll content of P. maackianus and P. crispus increased with decreasing water levels, while that of M. spicatum and E. nuttallii showed no significant change. The value of chlorophyll content of P. maackianus and M. spicatum was the highest and lowest at all water levels, respectively. The content of total chlorophyll of P. crispus was significant lower than that of E. nuttallii at 54 cm water depth, but other species had no significant difference. The soluble sugar of P. maackianus, P. crispus and E. nuttallii decreased with decreasing water level, while that of M. spicatum increased. The soluble sugar of M. spicatum was the highest and P. crispus was the lowest at both 54 cm and 36 cm depth. However, no significant differences of soluble sugar among four species were found at 18 cm water depth. The results suggest that extremely low water level had stressful impacts on M. spicatum but not on P. maackianus, P. crispus and E. nuttallii, and that the higher potential photosynthesis of E. nuttallii compared with native species would aid its invasive risk in shallow water in spring.