Abstract: More and more attention has being paid to the  pollution in waters induced by the fast growth of submerged macrophyte. In this paper, a laboratory simulation experiment was conducted to study the effects of different concentrations (0, 0.01, 0.02, 0.10, 0.20, 0.50, 0.75, 1.00, and 1.25 g·L^-1) of cycocel on the dwarfing characteristics and physiological indices of Vallisneria natans. After treated with different concentration cycocel for 30 days, the plant height of V. natans had significant differences (P<0.05). The higher the cycocel concentration, the higher the dwarfing effect was. Cycocel made V. natans leaves wider and its roots shorter. At 0.02-0.20 g·L^-1 of cycocel, the root/shoot ratio increased; at 0.01-0.50 g·L^-1 of cycocel, the plant number increased. At 0.10-0.50 g·L^-1 of cycocel, the wet weight of V. natans increased by 61%-123%, which meant that the plants could absorb more nutrients such as nitrogen and phosphorus from waters and sediments, and improve water quality. At 0.02 g·L^-1 of cycocel, the dwarfing effect was much better, and the plants occupied smaller space. Moreover, the plants at 0.02 g·L^-1 of cycocel had longer root length and higher root/shoot ratio, chlorophyll content,  SOD and POD activities,  accordingly, had an increased stressresistance and a delayed aging. In sum, 0.02 g·L^-1 of cycocel was more suitable for V. natans dwarfing.

Key words: trellis-cultivated melon, P fertilizer efficiency, P uptake, dry matter accumulation.