13:45 〜 14:00
[ACG37-01] Study of canopy Solar-Induced chlorophyll Fluorescence in a ground-based study in conjunction with Gross Primary Productivity in a subtropical evergreen forest
キーワード：SIF, subtropical forest
1.Background and objective
Photosynthesis in plants consists of two main processes: the light reaction and the carbon reaction. During the light reaction, the destiny of an absorbed photon can be as non-photochemical quenching (NPQ), photochemical quenching (PQ), or released as chlorophyll fluorescence. Solar-Induced chlorophyll Fluorescence (SIF) is defined as a small emission of redfarred light (650850 nm) from chlorophyll as a byproduct of the light reactions.
The total emitted SIF has been widely used to improve global gross primary productivity (GPP) estimation, while remote sensing observations of SIF could only capture a portion of the fluorescence process, and are often impacted by weather, which made it important to study the ground-based SIF measurements. Previous studies have found that the relationships between SIF and GPP are not simply linear and varies across vegetation types. However, the research of sub-tropical forest is very limited. Hence, the variations of SIF during days and seasons and the correlated factors of sub-tropical forests are crucial for scientific research.
2.Methods
The Yona site in Okinawa, Japan, is surrounded by evergreen broad-leaved forests. In this study, a high spectral resolution spectrometer (QEPro Grating H6) and a wide range spectrometer (Flame-S Grating #3) were installed in Yona since 2019 to detect SIF and estimating vegetation indices (VIs), respectively. Data between 2020 and 2022 were calculated in this study. Far-red SIF were retrieved using the spectral fitting method (SFM) in the O2-A absorption band (759-767 nm) of QEPro based on the open source package FieldSpectroscopyDP in R software. The estimated GPP measured using an eddy covariance method was used to examine the SIF variation as a proxy of photosynthetic activity.
3.Results
The diurnal averages change trends of Far-red SIF show a consistent trend across three years. Peaks in Far-red SIF are more frequent in April and August. In terms of seasonally averaged daily change trend, Far-red SIF reaches its highest levels during the summer across different seasons throughout the entire day. However, within a day, Far-red SIF peaks during the noon hours (11:00~13:00) in autumn, surpassing the levels observed across all seasons.
Overall, the liner regression analysis of daily mean Far-red SIF and GPP shows weak correlations across three years(R2 = 0.18). For different seasons, summer and winter averaged by three years were more strongly correlated(R2 = 0.33 and 0.29, respectively) than spring and autumn(R2 = 0.12 and 0.13, respectively). For further improvement, data with different time resolutions, such as half-hourly averaged SIF should be calculated to match the GPP for better analysis.
Photosynthesis in plants consists of two main processes: the light reaction and the carbon reaction. During the light reaction, the destiny of an absorbed photon can be as non-photochemical quenching (NPQ), photochemical quenching (PQ), or released as chlorophyll fluorescence. Solar-Induced chlorophyll Fluorescence (SIF) is defined as a small emission of redfarred light (650850 nm) from chlorophyll as a byproduct of the light reactions.
The total emitted SIF has been widely used to improve global gross primary productivity (GPP) estimation, while remote sensing observations of SIF could only capture a portion of the fluorescence process, and are often impacted by weather, which made it important to study the ground-based SIF measurements. Previous studies have found that the relationships between SIF and GPP are not simply linear and varies across vegetation types. However, the research of sub-tropical forest is very limited. Hence, the variations of SIF during days and seasons and the correlated factors of sub-tropical forests are crucial for scientific research.
2.Methods
The Yona site in Okinawa, Japan, is surrounded by evergreen broad-leaved forests. In this study, a high spectral resolution spectrometer (QEPro Grating H6) and a wide range spectrometer (Flame-S Grating #3) were installed in Yona since 2019 to detect SIF and estimating vegetation indices (VIs), respectively. Data between 2020 and 2022 were calculated in this study. Far-red SIF were retrieved using the spectral fitting method (SFM) in the O2-A absorption band (759-767 nm) of QEPro based on the open source package FieldSpectroscopyDP in R software. The estimated GPP measured using an eddy covariance method was used to examine the SIF variation as a proxy of photosynthetic activity.
3.Results
The diurnal averages change trends of Far-red SIF show a consistent trend across three years. Peaks in Far-red SIF are more frequent in April and August. In terms of seasonally averaged daily change trend, Far-red SIF reaches its highest levels during the summer across different seasons throughout the entire day. However, within a day, Far-red SIF peaks during the noon hours (11:00~13:00) in autumn, surpassing the levels observed across all seasons.
Overall, the liner regression analysis of daily mean Far-red SIF and GPP shows weak correlations across three years(R2 = 0.18). For different seasons, summer and winter averaged by three years were more strongly correlated(R2 = 0.33 and 0.29, respectively) than spring and autumn(R2 = 0.12 and 0.13, respectively). For further improvement, data with different time resolutions, such as half-hourly averaged SIF should be calculated to match the GPP for better analysis.