[A-CG37] Biogeochemical cycles in Land Ecosystem

[ACG37-08] Ground-Based Measurement of Solar-Induced Chlorophyll Fluorescence in Wetland by High-Spectral Resolution

*Kitpanuwat TANATARAKEREE¹, Tomomichi Kato^2,3, Tomoki Morozumi³, KANOKRAT BUAREAL², Masahito Ueyama⁴, Naohisa Nakashima³, Hideki Ninomiya², Lan Wu⁵ (1.Graduate School of Agriculture, Hokkaido University, 2.Graduate School of Global Food Resources, Hokkaido University, 3.Research Faculty of Agriculture, Hokkaido University , 4.Graduate School of Life and Environmental Science, Osaka Prefecture University, 5.Hainan University)

Keywords:Solar-Induced Chlorophyll Fluorescence , Gross Primary Production, Ground-Based Measurement, Wetland, High-Spectral Resolution

Solar-induced chlorophyll fluorescence (SIF) has been observed and discovered to relate linearly to gross primary production (GPP) in terrestrial ecosystem [Krause and Weis, 1991; Meroni et al., 2009; Frankenberg et al., 2011; Paul-Limoges et al., 2018]. However, SIF variations under different plant growth stages and sky conditions, and water table depth effects appear to limit the understandings about SIF-GPP relationship at the field-based measurement. It remains ambiguous linked to how this relationship is affected by varying changes of palnt growth stage, sky, and water table, especially for wetland where is a critical part of carbon sinks. We conducted the ground-base measurement of canopy-top SIF in wetland, Bibai Mire, northern Japan, Hokkaido (43º19'N, 141º48'E, 16 m above sea level) during the growing season (from March to November) in 2020, and examined its relationship to the eddy-covariance GPP [Ueyama et al., 2020]. QEPro spectroradiometer (range of wavelength 648-808 nm, the full width half maximum (FWHM) of 0.31 nm, Ocean Optics, Dunedin, FL, USA) and the spectral fitting method (SFM; Meroni and Colombo., 2006; Meroni et al., 2010; Mazzoni et al., 2012) were used for SIF retrievals at the oxygen absorption band (O₂-A, centered around 760 nm). SIF was captured by the spectra of downwelling and upwelling at the height of 2 meters above the ground by hemisphere spectroradiometer. The downward solar irradiance was estimated from cosine corrector fiber (CC fiber) from field of view (FOV) at 180º and the upward canopy-reflected radiance was received by bare fiber FOV 25º and CC fiber FOV 180º. The slope and correlation in positive linear regression between SIF and GPP were found to vary among the growth stages (slope = -2.99, 107.60, 62.57 and 47.97 (µmolmW^-1s^-1nm) and r² = 0.01, 0.41, 0.73 and 0.65 in Pre-Growing (DOY74-135), Growing (DOY144-179), Mature (DOY180-256) and Senescence (DOY260-295), respectively), suggesting that vegetation growth has a strong impact on the seasonal variations of canopy SIF and its realtion to GPP. In contrast, we found that sky conditions such as sunny (clearness index > 0.5) and cloudy (clearness index ≦ 0.5) have no clear influence on relationship of SIF and GPP (slope = 59.59 and 91.06 (µmolmW^-1s^-1nm) and r² =) and r² = 0.68 and 0.75 in sunny day and cloudy day, respectively).