[A-CG37] 陸域生態系の物質循環

[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

*両角 友喜¹、加藤 知道¹、辻本 克斗²、Buareal Kanokrat³、中島 直久¹、酒井 佑槙⁴、小林 秀樹⁴、奈佐原 顕郎⁵、秋津 朋子⁵、村山 昌平⁶、野田 響⁷、村岡 裕由⁸ (1.北海道大学　農学研究院、2.東北大学　生命科学院、3.北海道大学　国際食資源学院、4.海洋研究開発機構、5.筑波大学　生命環境系、6.産業技術総合研究所、7.国立環境研究所、8.岐阜大学　流域圏科学研究センター)

キーワード：クロロフィル蛍光、豪雨イベント、リモートセンシング、タワー観測

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.