Abstract
Solar-induced chlorophyll fluorescence (SIF) observations from space have shown close relationships with terrestrial photosynthesis rates. SIF originates from the light reactions of photosynthesis, whereas carbon fixation takes place during the dark reactions of photosynthesis. Questions remain regarding whether SIF is able to track changes in the efficiency of the dark reactions in photosynthesis. Using concurrent measurements of leaf-scale gas exchange, pulse amplitude-modulated (PAM) fluorescence, and fluorescence spectral radiances, we found that both far-red fluorescence radiances and PAM fluorescence yields responded rapidly to changes in photosynthetic carbon assimilation due to changes in environmental factors or induced stomatal closure under constant light conditions. Uncertainties in outgoing and incoming irradiance mismatch for SIF measurements may very likely obscure the contributions of the dark reactions, thereby causing the inconsistent findings previously reported, which were no change in far-red SIF and PAM fluorescence yields after clear reductions in the photosynthetic carbon assimilation efficiency of dark reactions. Our results confirm that high-quality SIF measurements have the potential to provide insights into the dark reactions of photosynthesis. This study is particularly relevant for better interpreting satellite SIF observations that are obtained under roughly constant overpass times and relatively stable light intensities.
Highlights
Most lives on Earth depend on energy from the sun
For the CO2 curves with constant irradiance, the proxies of photosynthetic capacity including AG and ΦPSII for soybean (Figure 3a,e) and maize (Figure 3c,g) increased with increasing CO2, until plateaus occurred at a CO2 concentration of about 500 ppm
Marrs et al [25] showed that leaf-scale fluorescence signals (SIF and fluorescence emission (Fs)) did not exhibit a clear trend after stomatal closure, suggesting that changes in Solar-induced chlorophyll fluorescence (SIF) emissions only responded to changes in the light reactions of photosynthesis
Summary
Most lives on Earth depend on energy from the sun. Photosynthesis is the only process that can convert light energy to chemical energy [1]. If the answer is yes, it indicates that SIF does provide direct insight into the processes occurring in the dark reactions, including gas exchange and carbon assimilation This has important implications for better understanding the SIF–GPP relationship when APAR is not a major limiting factor. Definitions leaf net CO2 assimilation (μmol m−2 s−1) leaf dark respiration (μmol m−2 s−1) leaf-scale gross photosynthetic CO2 assimilation estimated from the gas exchange system (μmol m−2 s−1) stomatal conductance to water vapor (mol m−2 s−1) maximum fluorescence yield induced by a saturation pulse in the dark-adapted state maximum fluorescence yield induced by a saturation pulse in the light-adapted state steady-state fluorescence yield from PAM photochemical quantum yield of PSII nonphotochemical quenching the total chlorophyll fluorescence radiance emitted from both abaxial and adaxial surfaces of a leaf at 760 nm (mW m−2 nm−1 sr−1)
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