Response Of Submerged Plant To Different Nutritional Conditions And Water Depth Gradient

Submerged plants is an important part of the lake ecosystem that have multiple functions,including controlling algae growth,purifying water quality and mediating material circulation.It plays an important role in stability and health of ecosystem.However,with the serious eutrophication and the frequent occurrence of extreme lake water level in recent years,have caused a recession of submerged vegetation directly or indirectly.Therefore,it is important to clear that the response of submerged plants to different nutrient conditions and the influence of submerged plants on the growth,physiology and photosynthetic characteristics.They are the keys in restoration and reconstruction of submerged vegetation and ecological restoration of eutrophic lake.The experiments were carried out from two aspects:water body nutrition and water depth environment in this paper to investigate the response characteristics of submerged macrophytes to water nutrition and water depth,providing a data base for submerged plant on restoration,reconstruction and management.The results ofNutrition simulation showed that the increased range of Vallisneria natans,Myriophyllum spicatum,Ceratophyllum demersum biomass in medium concentration(TN:1.40 mg·L^-1,TP:0.072 mg·L^-1)were maximum;Plant stem leaf index changing with water nutrition trends do not agree with root length change.The trend of the increased range of stem mass and leaf mass weren't agree with root length change.About the content of nitrogen and phosphorus,four kinds of submerged plant organs in the three concentration gradient keep the similar rules;nitrogen content:leaf>stem>root;phosphorus content in root>stem and leaves.About the accumulation of nitrogen and phosphorus,4 kinds of submerged plant leaf nitrogen accumulation ability obviously stronger than the stems and roots.The largest nitrogen accumulation under low concentrations(TN:0.47 mg·L^-1,TP:0.021 mg·L^-1)is Myriophyllum spicatum,and the phosphorus accumulation is Vallisneria natans,both suitable for planting to harvest under low concentration to remove nitrogen and phosphorus.The biggest accumulation of nitrogen and phosphorus are Ceratophyllum demersum in Medium and high concentrations?under medium concentration N:6587.37 mg/m2,P:744.63 mg/m2;under high concentration N:6096.63 mg/m2,P:692.36 mg/m2?,for transfering nitrogen and phosphorus in mowing as an ideal specie under higher nutrient level.The results of simulation experiment about water depth environment were as follows:?1?The increased gradient of water depth inhibited the growth rate of plant height;the maximum photosynthetic electron transport rate?ETRmax?decreased;the water transparency increased significantly;underwater photosynthetic active radiation?PAR?was exponential decay.?2?Potamogeton wrightii could adapt to the changes of water depth with strong extensibility in the height of it.?3?The SOD and POD in the leaves of the plants were different in different water depths,there was a similar trend between the two;the content of Chl-a:Potamogeton maackianus<Potamogeton wrigthtii,in addition the content of Chl-a in the leaves of Potmogeton wrightii was more sensitive to the change of water depth.?4?About survival rate,the tolerance of two submerged plants on the water depth showed:Potamogeton maackianus>Potamoge-ton wrightii.? The mortality rate of Microdia eyelets was more than 50%within 65 days under 3.5 m water depth;?Potamogeton wrightii died rapidly at the water depth of 3.5 m in a low concentration pool,the mortality rate was more than 50%within 30 days,all died within 45 days.?5?In a word,in the short period of time?<30 d?when Water level rising,Potamogeton wrightii had good adaptability to water depth and resistance to water stress,but the persistent deep water environment?water depth of 3.5 m or more?would lead to plant death;the morphological plasticity of Potamogeton maackianus to the change of water depth was less than Potamogeton wrightii.However,combining persistence monitoring results about plant height with the situation of survival to say the tolerance of water plants to water depth,the result was Potamogeton maackianus>Potamogeton wrightii.Potamogeton maackianus tolerated water depth of 3.5 m,Potamogeton wrightii tolerancd water depth of 3.0 m.