Based on the investigation of the species and frequency of submerged plants in Nanjishan Wetland of Poyang Lake in the winter of 2013,chlorophyll contents and photosynthetic fluorescence characteristics of the dominant submerged plants were studied using chlorophyll fluorescence imaging method. The results indicate that the major submerged plants of Nanjishan Wetland in Poyang Lake in winter included Hydrilla verticillata,Vallisneria natans,Najas minor,Potamogeton pectinatus,Nymphoides peltatum,Myriophyllum verticillatum and so on,and the dominant species were mainly H. verticillata and V. natans in different submerged plant communities. The chlorophyll content of H. verticillata is higher than that of V.natans,and the photosynthesis intensity of H. verticillata is stronger than that of V. natans. The value of Ca / Cb of H. verticillata is not large,which shows that the light-harvesting capacity of H. verticillata＇s chlorophyll is considerable in different sampling sites. The highest value of QY-max of V.natans is up to 0. 732,while the lowest value is only 0. 465; the highest value of QY-max of H. verticillata is 0. 677,while the lowest value is 0. 556.All values of QY-max of the submerged plants were lower than 0. 8,which shows that the submerged plants in Nanjishan Wetland of Poyang Lake may be subjected to certain external stress,which indicates that the external stress might cause some damage for the PSII reaction centers.
We used a FluorCam portable chlorophyll fluorescence imaging system to measure QY-max （the maximum light quantum yield, Fv/Fm, the largest light quantum efficiency of PS Ⅱ） of submerged plants in wetlands of Baisha Lake and Changhu Lake, Jiangxi Nanjishan Wetland National Nature Reserve, in winter 2013. Specifically, we measuredΦPS Ⅱ （PS Ⅱ actual quantum efficiency）, qP （photochemical quenching） and corresponding fluorescence images. Using the visual method and sampling sites method to obtain coverage, richness and abundance of submerged plants, and determined nutrient levels in water. The results show that the QY-max ofHydrilla verticillata andVallisneria natans in Baisha Lake ranged from 0.48 to 0.68 and 0.52 to 0.71, respectively; theΦPS Ⅱ of these two species ranged from 0.32 to 0.58 and 0.20 to 0.46, respectively. The two plants had similar photosynthetic efifciency. The QY-max ofNymphoides peltatum andV. natans in Changhu Lake ranged from 0.66 to 0.77 and 0.19 to 0.68, respectively; theΦPS Ⅱ of these two species ranged from 0.26 to 0.48 and 0.22 to 0.43, respectively. The observed higher photosynthetic efifciency of N peltatum suggests it is more likely to become the dominant species. In Baisha Lake, the frequency of occurrence of plants was：H. verticilata, 90%;V. natans, 93.3%;Najas minor26.7%, andPotamogeton francheti10%. In Changhu Lake, the frequency of N. pel-tatum was 86.7%,V. natans was 16.7%, andN. minor was 56.7%. The overal frequency of submerged plants living in Baisha Lake was much higher than that of submerged plants living in Changhu Lake, with different species dominating the two lakes. According to comprehensive analysis and comparison of trophic levels, biodiversity and photosynthetic fluorescence characteristics in the two lakes, eutrophication of Baisha Lake was higher than for Changhu Lake; andH. verticillata andV. natans were the dominant species, with similar photosynthetic activity. Conversely, in Changhu Lake,N. peltatum andV. natans were the dominant speci
