| Under the background of global change, the eutrophication and its influence on the lake ecosystem health has become one of the important research fields which focus on the relation between the global change and aquatic ecosystems. The natural growth and artificial planting of submerged plants play an important role in the remission of eutrophication and the purification of water. However, the increasing of UV radiation on the earth’s surface induced by the growing of O3concentration in the stratosphere, and its penetration in the water, has pronounced harms on aquatic plants. Therefore, the study focusing on the growth of submerged plants and its absorbency of nutrients under the increasing of UV radiation, and the propose of some parameters for the artificial planting of submerged plants such as density, depth, range and so on, have major and immediate significance and using value for the mitigation of eutrophication and the restore of aquatic ecosystems. This study focuses on Potamogeton crispus as the research object, by conducting indoor cultivation experiments, and discusses characteristics of the growth and absorption kinetics for nitrogen and phosphorus of Potamogeton crispus. On this basis, a set of evaluation index system of integrated effects is proposed to quantify the effect of effects of UV-B radiation on Potamogeton crispus, and critical growing depth for Potamogeton crispus is found out by combining the research findings on the penetration and attenuation of UV-B radiation in the water.Main conclusions of the study are listed as follows:(1) Under low-intensity UV-B radiation (<105μW/cm2) condition, at the initial phase, the biomass of the of Potamogeton crispus declines and can be recovered as the growth continues declining to slow decline phase. Under125μW/cm2radiation, the biomass decreases to minimum values which cannot be restored, but continues to decline in the fall period. At low doses of UV-B radiation (≤105μW/cm) conditions, UV-B radiation can promote increasing the leaf chlorophyll concentration, but will act as a disincentive after entering a period of decline.(2) When UV-B radiation is lower than105μW/cm2, the activity of ACP and NR enzyme increased, which could be an important adaptive mechanism of UV-B radiation stress. Within the65～125UV-B (μW/cm2, the affinity of Potamogeton crispus for NO3-and the absorption rate decrease. Under the conditions of65～125UV-B μW/cm2, the affinity of Potamogeton crispus for NH4+the affinity and its absorption rate increases with the intensity of UV-B radiation gradually. When the UV-B radiation is during0-125μW/cm2, with the increasing of UV-B radiation, the affinity for PO43-declines. When the UV-B radiation is65-125μW/cm2, the PO43-absorption rate of Potamogeton crispus decreases.(3) When UV-B radiation is lower than85μW/cm2, enhanced UV-B radiation has little effect on the decomposition rate of Potamogeton crispus. Meanwhile, when the UV-B radiation is65μW/cm2, Potamogeton crispus has the maximum decomposition rate. When the UV-B radiation is higher than105μW/cm2, UV-B accelerates the decomposition of corruption in the decline and fall of Potamogeton crispus and the decomposition rate increases with the intensity of UV-B radiation.(4) Low-intensity UV-B radiation (≤105μW/cm2) has little effect on the releasing of nitrogen. When the intensity of UV-B radiation is higher than105uw/cm2, the releasing of nitrogen increases. When the UV-B radiation intensity is higher than105μW/cm2, UV-B radiation accelerates the decline of Potamogeton crispus but also promotes the release of phosphorus, and the strength of phosphorus release increases with the enhancement of UV-B radiation.(5) When the intensity of UV-B radiation is lower than85μW/cm2, sediments become systems-nitrogen sink, and some nitrogen in the system eventually migrated to sediment. When the UV-B radiation intensity is higher than105μW/cm2, the overlying water becomes the nitrogen sink, and the nitrogen of the system ultimately migrated to overlying water. When UV-B radiation intensity is higher than105μW/cm2, the overlying water system becomes phosphorus sink. When the intensity of UV-B radiation is125μW/cm2, the sediment becomes the system of phosphorus source, and part of phosphorus in the system eventually migrated to overlying waters.(6) Based on some of the research results in this article, a set of enhanced UV-B radiation on the growth of Potamogeton crispus evaluation index system was proposed, indicators of the index system of rating per unit time rates of change calculated effect sizes, integrated effects resulting from weighted summation index (IEI), quantitative analysis of UV-B radiation on the growth effects of Potamogeton crispus. |
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