BGD Biogeosciences Discussions BGD Biogeosciences Discuss. 1810-6285 Göttingen, Germany 10.5194/bg-2022-131 Impact of sky conditions on net ecosystem productivity of a “floating blanket” wetland in southwest China Shao Yamei 1 2 Liu Huizhi 1 2 Du Qun https://orcid.org/0000-0002-2273-1854 1 2 Liu Yang 1 2 Sun Jihua 3 Li Yaohui 4 State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China University of Chinese Academy of Sciences, Beijing 100029, China Yunnan Meteorological Observatory, Kunming 530100, China College of Aviation Meteorology, Civil Aviation Flight University of China, Guanghan 618307, China National Natural Science Foundation of China 91937301 Ministry of Science and Technology of the People's Republic of China 2019QZKK0105 National Natural Science Foundation of China 41975017 41905010 25 07 2022 2022 1 27 Copyright: © 2022 Yamei Shao et al. 2022 This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/ This article is available from https://bg.copernicus.org/preprints/bg-2022-131/ The full text article is available as a PDF file from https://bg.copernicus.org/preprints/bg-2022-131/bg-2022-131.pdf

<p>Based on eddy covariance (EC) measurements from 2016 to 2020, the impact of sky conditions on net ecosystem productivity (NEP) over Beihai wetland was examined. Sky conditions were classified into sunny, cloudy and overcast skies. On half-hourly timescale, the daytime NEP responds to the changing total photosynthetically active radiation (PAR<sub>t</sub>) more efficiently under cloudy and overcast conditions than sunny conditions across seasons. Compared with sunny conditions, the apparent quantum yield (&alpha;) under overcast (cloudy) conditions increased 342.9 % (271.4 %) in spring, 17.6 % (20.6 %) in summer, 280.0 % (230.0 %) in autumn and 125.0 % (25.0 %) in winter, respectively. Unlike the patterns of half-hourly NEP, the daily NEP was significantly lower under overcast conditions than that under cloudy and sunny conditions. And the daily NEP peaked under cloudy skies when the clearness index (CI) fluctuated around 0.3&ndash;0.6. Additionally, the ecosystem light use efficiency (LUE) and water use efficiency (WUE) also changed with the variations in sky conditions. The daily LUE and WUE reached their maximum values under overcast (CI: 0&ndash;0.2) and cloudy conditions (CI: 0.2&ndash;0.4), respectively. NEP was mainly controlled by the diffuse photosynthetically active radiation (PAR<sub>d</sub>) and air temperature (Ta), and the direct photosynthetically active radiation (PAR<sub>b</sub>) had a secondary effect on NEP from half-hourly to monthly timescales. Path analysis revealed that PAR<sub>b</sub> and Ta were the main controls affecting NEP under sunny conditions. While under cloudy and overcast conditions, PAR<sub>d</sub> was the most responsible for the variations of NEP.</p>