Water Level And Harvest The Research On The Effects Of Submerged Plant Growth

In the lakes situated in the monsoon region of China, the water levels varied seasonably, usually lower in spring and higher in summer. Based cn the natural variations, most aquatic plants could well germinate and have the good stability. However, due to the human activities, the seasonal regularity of water levels in many lakes have been greatly disturbed and even fluctuated oppositely in some lakes. Higher water level leading to the lack of enough sunlight in spring is harmful for the germination of submerged macrophytes and the growth of spears. While, lower water levels could also cause the overgrowth or even the death of bottomland plants. Water levels’effect on the bottomland has become a hot topic nowadays. To identify the effects that water levels and cutting strength on the growth and reproduction of submerged macrophytes, the experiments with submerged macrophytes in different water levels and the experiments with different water fluctuations and cutting intensity were conducted. The aim of this thesis is to provide theoretical basis for the recovery and scientific management of submerged macrophytes. The results showed below:(1) Water level fluctuation rates had significant effects on the growth of Potamogeton malaianus. With water level fluctuated, the number of withered leaves increased while the biomass decreased significantly in the groups. When water level fluctuation rates was at40,80and120cm/5d, maximum quantum yield (Fv/Fm) of P. malaianus was higher than that of the control group on the30th day, and then the Fv/Fm decreased when water level fluctuations rates was at160,200cm/5d. The maximum electron transport rate (ETRmax) of P. malaianus significantly decreased under the conditions of water level fluctuations.(2) Different water depths showed no significant influence on the germination of Potamogeton crispus and Hydrilla verticillata. The germination rate of P. crispus’s turions was higher than73.3%while the germination rate of winter buds of H. verticillata was higher than96.7%.(3) Different water depths had significant effects on the growth of seedlings of P. crispus and H. verticillata, and the higher water levels was not conducive to the growth of submerged plants’ seedlings. P. crispus and H. verticillata adapted themselves to different light conditions under water through changing the phenotypic plasticity and chlorophyll content. The number of tillers of P. crispus decreases while its chlorophyll content increased with the increase of water depths. The height of the plants increased among the depth from0.5to2.5m while it significantly reduced when the water depth was higher than3.0m. The height of the plants, the number of eustipes, the length of internodes and thenumber of branches and other morphological indexes of H. verticillata weregreatly different. The chlorophyll content of H. verticillata increased first andthen decreased. Fv/Fm of H. verticillata had no significant differences among each group. ETRmax of H. verticillata also had no obvious differences when the water depths were from0.5to1.5m while it decreased tremendously when the water depth was more than2m. H. verticillata was dead when water depth was more than3m due to the insufficient light.(4) The simulation experiment of water level manipulation showed that the increase of water levels had obvious effects" on the growth of seedlings of H. verticillata and Vallisneria spiralis. The biomass of H. verticillata significantly decreased while the water level increased. The seedling died after being moved quickly down to the deepest sites at4m depth and the luminous intensity was less than1%. When the water level increased in the moderate speed and stoped at the depth of2m and3m under water surface, the H. verticillata seedlings grew faster by increasing intermodal distance and decreasing divarications. When the water level increased in very low speed and stoped at the depth1m under water surface, the H. verticillata seedlings grew very quickly with much more divarication and large canopy. The plant under water grew fast for the low water level and enough light. V. spiralis adapted well to the increasing water depth by reducing the number of tillers and root-shoot ratio, and instead of extending the leaf length and increasing chlorophyll content, etc. But all the V. spiralis died when the water level at high-speed increase (80,100cm/5d).(5) Different cutting intensity had significantly effects on the growth and propagation of P. crispus and H. verticillata. After the low-intensity cutting (15,30cm), all P. crispus or most of them can recover in a short time while their abilities to recovery obviously decreased after the medium and high-intensity cutting (more than45cm). Cutting had obviously decreased the biomass of P. crispus and the quantity of the brood bud. Cutting with medium and low intensity (15-75cm) did not have obvious impacts on Fv/Fm of P. crispus while Fv/Fm of high intensity cutting group (90、105cm) reduced significantly. The maximal relative electron transport rate (ETRmax) of the leaves’Rapid Light Curves had no significant differences. Cutting with medium and low intensity did not have obvious impacts on the growth of H. verticillata and all of them can recover although the recovery time extends with the increase of cutting intensity. Cutting had obvious effects on biomass removal and control of H. verticillata and it significantly reduced the number of winter buds. H. verticillata can not form winter buds when cutting intensity was at90,105cm. At the beginning, cutting did not form significant inhibition on the growth of H. verticillata generally and the actual photochemical efficiency did not decrease significantly.