Estimation of gross primary production and light use efficiency by the tower-based sun-induced fluorescence measurement in the Japanese evergreen coniferous forest

Abstract:

Chlorophyll fluorescence (ChlF) is emitted from chlorophyll a and b to release the excess sun-light energy. Recently, ChlF has been utilized to represent the ecosystem photosynthetic activity, i.e. gross primary production (GPP), by the satellite remote-sensing studies (e.g. Frankenberg et al., 2011). Despite its high expectation, small number of ecosystem-level ChlF observation at the ground reduces its availability. The aim of this study is to clarify the relationships between ChlF, and photosynthesis and light use efficiency (LUE) by the ground based measurement in the forest. The observations were carried out in the evergreen coniferous forest in Takayama, Japan, from March 2008 to February 2009. Downward and upward spectral radiances were measured with hemispherical spectroradiometer (MS-700, Eko Instruments, Japan) mounted at 30m-high above the ground surface. We calculated Sun-Induced fluorescence (F_S) around the O₂-A band (760 nm) from the spectral data with the Fraunhofer Line Depth method. The GPP was calculated from the carbon fluxes measured with eddy covariance at the top of the tower. F_S showed the strong correlation to GPP linearly in the diurnal course (sunny day (8 August, 2008): r² = 0.81, cloudy day (28 July, 2008): r² = 0.87). In addition, GPP was fitted against F_S by rectangular hyperbolic curve. (r² = 0.87 (daily)). We also investigated the relationship between F_S and LUE in daily averages. The F_S-LUE relationship could be regressed by logarithm curve for each month (r² = 0.46 ˜0.95). The seasonal changes in the regression coefficients for F_S-GPP and F_S-LUE curves were thought to be induced by the seasonal variation in the temperature-dependency of photosynthesis and the phenology. We conclude that F_S can be utilized to estimate GPP and LUE in evergreen forest, and that relationship between F_S and GPP is influenced by environmental factors such as PAR and air temperature.Chlorophyll fluorescence (ChlF) is emitted from chlorophyll a and b to release the excess sun-light energy. Recently, ChlF has been utilized to represent the ecosystem photosynthetic activity, i.e. gross primary production (GPP), by the satellite remote-sensing studies (e.g. Frankenberg et al., 2011). Despite its high expectation, small number of ecosystem-level ChlF observation at the ground reduces its availability. The aim of this study is to clarify the relationships between ChlF, and photosynthesis and light use efficiency (LUE) by the ground based measurement in the forest. The observations were carried out in the evergreen coniferous forest in Takayama, Japan, from March 2008 to February 2009. Downward and upward spectral radiances were measured with hemispherical spectroradiometer (MS-700, Eko Instruments, Japan) mounted at 30m-high above the ground surface. We calculated Sun-Induced fluorescence (F_S) around the O₂-A band (760 nm) from the spectral data with the Fraunhofer Line Depth method. The GPP was calculated from the carbon fluxes measured with eddy covariance at the top of the tower. F_S showed the strong correlation to GPP linearly in the diurnal course (sunny day (8 August, 2008): r² = 0.81, cloudy day (28 July, 2008): r² = 0.87). In addition, GPP was fitted against F_S by rectangular hyperbolic curve. (r² = 0.87 (daily)). We also investigated the relationship between F_S and LUE in daily averages. The F_S-LUE relationship could be regressed by logarithm curve for each month (r² = 0.46 ˜0.95). The seasonal changes in the regression coefficients for F_S-GPP and F_S-LUE curves were thought to be induced by the seasonal variation in the temperature-dependency of photosynthesis and the phenology. We conclude that F_S can be utilized to estimate GPP and LUE in evergreen forest, and that relationship between F_S and GPP is influenced by environmental factors such as PAR and air temperature.