Research On The Growth And Chlorophyll Fluorescence Characteristics Of Wetland Submerged Plants Under Different Environmental Conditions

Environmental pollution has become a universal phenomenon with the rapid development of current industry. Water resource is accounted for 71 percent of the Earth, and its pollution prevention and control has become one of the urgent problems to be solved. Wetland ecosystem is one of the world’s three major ecosystem types, it is an unique ecosystem, which formed by the interaction of water and land. Submerged plants are the important parts of aquatic ecosystem, because they are completely submerged in the water, their survival, growth and reproduction were closely related to the aquatic environmental factors. In this study, we analyzed the growth and chlorophyll fluorescence characteristics of the submerged plants under different environmental conditions thorough two ways included field investigation in the natural wetland and indoor cultivation experiment. We aimed to provide some reference for the reconstruction of submerged plant communities in the degraded wetland and restoration of aquatic ecosystem function. This research paper get the support and funding by the national natural science foundation of China(D41161035): "The community structure of submerged plant in Poyang Lake wetland and its typical factor of water environment quantitative research".In this paper, on one hand, we investigated the typical lakes named Baishahu and Changhu which is located in Jiangxi Nanjishan Wetland National Reserve in Southern Poyang Lake, and studied the spatial distribution of submerged plants and their growth and chlorophyll fluorescence characteristics under the natural wetland conditions in different seasons of winter,spring, summer and autumn from November in 2013 to October in 2014. We used a Fluor Cam portable chlorophyll fluorescence imaging system to measure the parameters of the largest light quantum efficiency of PSII(QY_max), steady closed degree of PSII reaction centers(1-Qp Lss), steady non-photochemical quenching(NPQ_Lss) and corresponding fluorescence imaging of the submerged plants in different seasons. On the other hand, we adopted clean river sand and water culture methods to study the influences on H. verticillata under the different five kinds of concentration levels of Copper, Plumbum and Cadmium pollution stress separately. We study the all influences on H. verticillata included the stress on height, biomass,chlorophyll content and survival ratios of H. verticillata, as well as the effects of fluorescence parameters such as minimal fluorescence(Fo), maximal fluorescence(Fm), PSII maximum quantum yield(QY_max), degree of PSII reaction centers closed under stable state(1-Qp_Lss),non-photochemical quenching under stable state(NPQ_Lss) and fluorescence imagines of H.verticillata leaves, and we also discussed the variation characteristic of each parameter of H.verticillata under the stress of increasing concentrations of copper, plumbum and cadmium separately. The results and conclusions are as follows.(1) The results of the field investigation of the wetland in Poyang Lake show that the frequency distribution, chlorophyll contents, photosynthesis chlorophyll fluorescence parameters and imaging of submerged plants included H. verticillata, Vallisneria natans, Najas minor and other submerged plants of sampling sites in four seasons are highly or different related to the water environmental factors. Wetland water level depth and tra nsparency are the main most important factors which determine the distribution of subm erged plants, diversity, chlorophyll content, photosynthetic fluorescence characteristics. In this study, we found that the species diversity of submerged plants is more higher in S pring or Autumn than that of submerged plants in Summer or Winter. The Water level depth changed from 25 to 70 cm in Spring and changed from 50 to 170 cm in Autum n, and the water transparency value changed from 25 to 65 cm in Spring and changed from 10 to 65 cm in Autumn respectively. The Water level depth changed from 190 to250 cm and the water transparency value changed from 45 to 140 cm in Summer. The dominant species of H. verticillata and N. minor are suitable for rapid growth in Summer.The maximum quantum yield of PS(QY_max) of H. verticillata changed from 0.55 to 0.76 and that of N. minor changed from 0.74 to 0.78 respectively in Summer. The photo synthesis of V. natans is more higher in Spring than those in other seasons. The maxim um quantum yield of PS(QY_max) of V. natans changed from 0.34 to 0.62. The paramet er of Non photochemical quenching(NPQ_Lss) of H. verticillata, V. natans or N. minor and other submerged plants changed significantly in both space and time, which reflected the light protective capacity to avoid plant light system damage in the face of adversity.The values of Non photochemical quenching(NPQ_Lss) of the above plants are the most in Winter, and the mean values of Non photochemical quenching(NPQ_Lss) of H. verticillata, V. natans and N. minor are 1.28、0.73 and 1.83 respectively.(2) The results of the photosynthetic physiological indexes, fluorescence parameters and imaging characteristics of H. verticillata which were cultured in clean river sand and water indoor under the stress of heavy metals pollution stress show significant diff erence. On one hand, we found the results showed that the height and the dry weight of H. verticillata decreased significantly under the different levels of pollution stress of the heavy metal cadmium. This indicated that cadmium pollution might damage the bundle structure of H. verticillata. The effect of copper pollution on the dry weight of Hverticillata was far more prominent than the effect of cadmium pollution. All chlorophyl l values decreased significantly when the plants were subjected to the stress of cadmiu m or copper pollution, and the toxicity of copper pollution on the H. verticillata chloropl ast is greater than that of cadmium pollution. The chlorophyll fluorescence parameters(i ncluding Fo, Fm and QY_max) of H. verticillata under the stress of cadmium and cop per pollution were significantly lower than those of the control groups, but the values of(1-Qp_Lss) rose, and the values of NPQ_Lss first rose and then fell as the concentr ations of the heavy metals rose. On the other hand, the results also indicated that the i nfluence of Cadmium on H.verticillata was greater than the influence of Copper or Plum bum on H. verticillata in the same concentration. When the concentration of Pb2+ was l ower than 5 mg/L in water, the growth and photosynthesis of H. verticillata could appr oach to normal, which meant that H. verticillata could be used as purification species t o water bodies in which the concentration of Pb2+ was lower than 5mg/L. When the co ncentration of Cu2+ was lower than 1 mg/L in water, the growth and photosynthetic acti vities of H. verticillata could approach to normal, which meant that H. verticillata coul d be used to recover the water environment of low concentration of Copper contaminat ion. H. verticillata could not survive long time in the water environment with reache d or exceeded 3 mg/L Cadmium contamination, which meant that H. verticillata could be uesed as the water environmental indicator species with Cadmium contamination.In summary, There are many other environmental factors can impact on the photosynth esis of submerged plants such as water level, water transparency, total nitrogen and total phosphorus, heavy metals or other pollutants in water. Different environmental factors can effect on the chlorophyll contents, photosynthetic activity and other kinds of fluorescence parameters of submerged plants in some different degree. In addition, each environmental factor can contribute to the growth of submerged plants in the most suitable ecological range.