Observation Of Sunlight-Induced Chlorophyll Fluorescence In Poyang Lake Wetland

Poyang Lake is affected by the Yangtze River,which results in the great change of water level.The alternation of high and low water levels leads Poyang Lake to present a unique natural landscape of alternating land and water phases,and it has a huge impact on ecological functions such as carbon and water fluxes in the Poyang Lake wetland ecosystem.Solar-Induced Chlorophyll Fluorescence(SIF)provides a new and direct measurement method for estimating the photosynthetic carbon sequestration capacity of vegetation and water bodies.Therefore,the SIF observation research of Poyang Lake wetland ecosystem can provide an important reference for the carbon cycle of the lake wetland ecosystem,and also provide important scientific data for the study of the response of the wetland ecosystem carbon cycle change to climate change.Based on the SIF automatic observation system of Poyang Hunanji Wetland Station,this study continuously observed the SIF of the Poyang Hunanji wetland ecosystem from April 2020 to July 2021,and analyzed the variation characteristics of the SIF of the Poyang Lake ecosystem during the wet season and the dry season.Combining with the changes of environmental elements in Poyang Hunan Ji Wetland Comprehensive Experiment Station,the main influencing factors of SIF changes in Poyang Lake wetland ecosystem were analyzed and discussed.The main conclusions of the paper are as follows:(1)The SIF,spectrum,flux and meteorological observation data of the Poyang Lake wetland ecosystem for two consecutive years from 2020 to 2021 were obtained.During the dry season of Poyang Lake(Nanji Wetland Station was covered by vegetation),the 3FLD algorithm was used to invert the SIF continuous observation data under the vegetation coverage of the wetland station;during the wet season of Poyang Lake(Nanji Wetland Station was covered by water body),assuming the inversion results of the 3FLD algorithm as the "true value",the applicability of the FLH algorithm for different spectral resolution conditions in the detection of SIF in water bodies during the wet season was quantitatively evaluated.The results indicated that the SIF inversion of FLH algorithm under the condition of 3 nm spectral resolution is in a good agreement with the results of 3FLD algorithm.The SIF continuous observation data under the water coverage state of the wetland station were calculated.(2)The diurnal and seasonal changes of SIF in Poyang Lake wetland ecosystem were elucidated.The results of diurnal and seasonal changes in wetland vegetation SIF in dry season showed that the diurnal variation trend of wetland vegetation coverage SIF in sunny days presents a similar law,that is,the diurnal variation curve of SIF exhibits a single-peak feature,and the peak appeared around 12:00 noon;The seasonal variation of wetland vegetation SIF was more significant in the dry season,the SIF of wetland vegetation was higher in spring,and the daily average SIF was about 0.4mW/m~2/nm/sr;the SIF of wetland vegetation in winter was lower,and the daily average SIF was about 0.1mW/m~2/nm/sr.The diurnal and seasonal changes of SIF in wetland water body during wet season showed that the diurnal variation trend of SIF covered by wetland water body also gave a similar law,that is,the diurnal variation curve of SIF showed a single peak characteristic,and the peak appeared around 12:00 noon;The seasonality of SIF in wetland water body was not significant during wet season,and the daily average SIF was between 0.2 and 0.35 mW/m~2/nm/sr.(3)The environmental response law of Poyang Lake wetland ecosystem SIF was analyzed.Based on the continuous observation data of the Poyang Lake wetland ecosystem,the temporal dynamic changes of meteorological factors such as temperature,rainfall,and photosynthetically active radiation were analyzed,and the effects of these meteorological factors on SIF during dry and wet periods were explored.The results showed that when the wetland station was covered by vegetation in the dry season,there was an obvious positive correlation between PAR and SIF.The R~2 of the clear sky diurnal variation data can reach a maximum of 0.98,the R~2 of all the data during the observation period was 0.78,and the partial correlation coefficient was 0.73.Compared with temperature and precipitation,PAR was the dominant environmental factor for the change of wetland vegetation SIF;under the condition of water coverage of wetland stations in wet season,there was also a strong positive correlation between clear sky PAR and SIF,and the R~2 of clear sky diurnal variation data was 0.79,the R~2 of all data during the observation period was 0.57,and the partial correlation coefficient was 0.79,which indicated that PAR was also the dominant environmental factor of wetland water body SIF,compared with temperature and precipitation.