[A-CG37] Biogeochemical cycles in Land Ecosystem

[ACG37-P06] Seasonal variation in Solar Induced chlorophyll Fluorescence detected by multi-vertical layer spectroscopy in a canopy of cool-temperate deciduous broadleaf forest in Takayama, Gifu

*Tomoki Morozumi¹, Tomomichi Kato¹, Katsuto Tsujimoto², KANOKRAT BUAREAL³, Naohisa Nakashima¹, Yuma Sakai⁴, Hideki Kobayashi⁴, Kenlo Nasahara⁵, Tomoko Akitsu⁵, Shohei Murayama⁶, Hibiki M Noda⁷, Hiroyuki Muraoka⁸ (1.Research Faculty of Agriculture, Hokkaido University, 2.Graduate School of Life Sciences, Tohoku University, 3.Graduate School of Global Food Resources, Hokkaido University, 4.Institute of Arctic Climate and Environment Research, Japan Agency for Marine-Earth Science and Technology, 5.Faculty of Life and Environmental Sciences, University of Tsukuba, 6.Environmental Management Research Institute, National Institute of Advanced Industrial Science and Technology, 7.Center for Global Environmental Research, National Institute for Environmental Studies, 8.River Basin Research Center, Gifu University)

Keywords:Chlorophyll Fluorescence, Heavy Rain Event, Remote Sensing, Tower Observation

Solar Induced chlorophyll Fluorescence (SIF) is a quantitative remote sensing signal relating to the photosynthetic activity including gross primary productivity (GPP) of terrestrial ecosystems. After excitation by solar photon, chlorophyll pigment emits a part of unusable excess energy as fluorescence, which equals to SIF. On the contrary to other remote sensing vegetation indices (VIs), SIF has an advantage to be able to explain both diurnal and seasonal GPP variations with relating to photosynthetic active radiation (PAR), leaf absorptance, and photochemical reaction. Previous studies in a deciduous broadleaf forest argued that decrease at the canopy top VIs had lagged after that in the photosynthetic capacity in senescence period, although understory photosynthesis could be activated after crown leaf-off. Recent heavy rainfall events also may affect photosynthetic activity. Therefore, rapidly responding SIF can be expected to be an aid of monitor real-time suppression of photosynthetic activity in the vertical layer of forest canopy. The purpose of this study is to examine whether the ground-based SIF could respond at an autumn-winter senescence period and rainfall events when GPP supposed to decline. We continuously observed ultra-fine (full width at half maximum < 0.4 nm) spectral radiation in a deciduous broadleaf forest ecosystem, at TKY flux site (36.15°N, 137.42°E), Takayama, Gifu since August 2019 to December 2020. A spectrometer (QEpro, Ocean Optics, Dunedin, FL, USA) was equipped of 7 optical fiber cables via optical fiber switch and captured the upward and downward spectral radiation at three heights: 8, 14, and 18m (canopy top) with field of view (FOV) of 180° and FOV of 25°. SIF was retrieved using spectral fitting method for O₂-A absorption band (759-767 nm). Half-hourly SIF varied 1.5-0.5 to 0.1-0 (mW m^-2 nm^-1 sr^-1) from summer to winter. Decreasing SIF besides almost stable VIs variations were shown at heavy rainfall events in late September 2019 and in early July 2020. A timing of SIF decline was earlier at the canopy top, and SIF signal remained detectable from understory till the end of senescence period. The result also suggests that there is a potential contribution of evergreen understory (< 8 m) in snowless winter periods.