Ground-based observation on Solar-induced chlorophyll fluorescence in rice ecosystem with high-spectral resolutions

Abstract:

Solar-Induced Chlorophyll fluorescence (SIF) is considered to be a desirable remote-sensing proxy for tracking photosynthesis in recent decades. Although several studies implied that SIF related to photosynthesis activities and Gross primary productivities (GPP) from single leaf measurement toward a global scale by satellite (e.g. GOSAT, FLEX), the validation of SIF at the ecosystem level in both spatial and temporal scale should be more concurrently considered for developing a higher accuracy model of global carbon cycling and broaden the understanding on SIF and GPP relationship. This study focuses on the ground-based investigating SIF in the paddy field (Oryza sativa L.; cultivar Koshihikari) ecosystem, which is one of the major crops in Asia. The QEPro (high spectral resolution with 0.3 nm full width at half maximum; Ocean Optics, Dunedin, FL, USA) was installed in Mase eddy flux site (36.05°N, 140.03°E, 11 m ASL.) in June to September (one growing season) 2019 in Tsukuba, Japan. The optical fiber splitter (LEONI Fiber Optics GmbH, Föritztal, Germany) was connected to a spectroradiometer and three optical fibers to switch the optical fiber channels and the spectrum was measured with 5 minutes interval time. The upwelling reflected radiance from the paddy field was detected by optical fiber with cosine corrector field of view (FOV) at 180° and bare fiber FOV 25°, and the downwelling irradiance was detected with FOV 180°. The Spectral Fitting Method (SFM; Meroni et al., 2009) was used to retrieve the SIF signal. The results present a strong correlation between SIF and GPP in both diurnal and seasonal scales. The diurnal variation of SIF linearly correlated with the GPP with the coefficient of determination (r²) of 0.75. Regarding seasonal relationships, SIF showed a strong correlation with GPP (r²=0.61), and Normalized Difference Vegetation Index (NDVI; r²=0.53), especially in sunny conditions. It seems that the sky condition influences SIF signal. It is noted that SIF has the potential to be recognized as a proxy of photosynthesis in the paddy field ecosystem.