During photosynthesis, absorbed photon energy may be used in three alternative pathways: photochemistry, heat loss (nonphotochemical quenching, NPQ), or re-emitted as chlorophyll a fluorescence (ChlF, SIF if at the canopy scale) in the spectral range 640–850 nm. A number of studies have shown that SIF observations have a strong correlation with gross primary production (GPP) in a variety of terrestrial ecosystems. However, SIF-GPP relationships are mostly built by statistically relating top-of-canopy (TOC) SIF observations (SIFTOC) to eddy covariance flux-tower GPP estimates.
Prof. Lu and his students developed a process-based model, based on the mechanistic light response (MLR) model, to mechanistically link SIFTOC with the photosynthetic activity of vegetation.Specifically, they 1) reformulated the equations by replacing the fraction of open PSII reaction centers (qL) and the maximum quantum yield of photosystem II (ФPmax) with nonphotochemical quenching (NPQ) and the quantum yield of photosystem II (ΦP); 2) reconstructed hemispherical broadband SIF fluxes at photosystem II (PSII) from the directional observed SIFTOC that is contributed from photosystem I and II; 3) estimated other key parameters including KDF (ratio between the rate constants for constitutive heat loss and fluorescence), Cc (chloroplastic CO2 partial pressure), and Γ* (chloroplastic compensation point of CO2). A comparison against flux-tower based GPP at a winter-wheat study site demonstrated that the modeled GPP is able to quantify canopy photosynthesis with good accuracy at both half-hourly(R2 = 0.85, RMSE = 5.62 μmol m-2 s-1, rRMSE = 9.10%) and daily (R2> 0.90, RMSE = 3.25 μmol m-2 s-1and rRMSE = 8.69%) scales. This progress enhances our ability to mechanistically estimate GPP with SIF at the canopy scale, an essential step to model carbon uptake using satellite SIF at regional and global scales.
Dr. Liu, zhunqiao, a postdoctoral researcher in Lu’s group is the first author, Prof. Lu is the corresponding author. The other authors include Prof. Cai, huanjie and Prof. Yu, qiang from Northwest A&F University, Prof. Zhao, feng from Beihang University, and Prof. Liu, xinjie from Chinese Academy of Sciences. This work is supported by the National Natural Science Foundation of China (Grant No. 41901293, 42071328, and 41771382), the China Postdoctoral Science Foundation (Grant No. 2019M663828), and the Chinese Universities Scientific Fund (24520212452021125).
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Remote Sensing of Environment
During photosynthesis, absorbed photon energy may be used in three alternative pathways: photochemistry, heat loss (nonphotochemical quenching, NPQ), or re-emitted as chlorophyll a fluorescence (ChlF, SIF if at the canopy scale) in the spectral range 640–850 nm. A number of studies have shown that SIF observations have a strong correlation with gross primary production (GPP) in a variety of terrestrial ecosystems. However, SIF-GPP relationships are mostly built by statistically relating top-of-canopy (TOC) SIF observations (SIFTOC) to eddy covariance flux-tower GPP estimates.
Prof. Lu and his students developed a process-based model, based on the mechanistic light response (MLR) model, to mechanistically link SIFTOC with the photosynthetic activity of vegetation. Specifically, they 1) reformulated the equations by replacing the fraction of open PSII reaction centers (qL) and the maximum quantum yield of photosystem II (ФPmax) with nonphotochemical quenching (NPQ) and the quantum yield of photosystem II (ΦP); 2) reconstructed hemispherical broadband SIF fluxes at photosystem II (PSII) from the directional observed SIFTOC that is contributed from photosystem I and II; 3) estimated other key parameters including KDF (ratio between the rate constants for constitutive heat loss and fluorescence), Cc (chloroplastic CO2 partial pressure), and Γ* (chloroplastic compensation point of CO2). A comparison against flux-tower based GPP at a winter-wheat study site demonstrated that the modeled GPP is able to quantify canopy photosynthesis with good accuracy at both half-hourly(R2 = 0.85, RMSE = 5.62 μmol m-2 s-1, rRMSE = 9.10%) and daily (R2 > 0.90, RMSE = 3.25 μmol m-2 s-1 and rRMSE = 8.69%) scales. This progress enhances our ability to mechanistically estimate GPP with SIF at the canopy scale, an essential step to model carbon uptake using satellite SIF at regional and global scales.
Dr. Liu, zhunqiao, a postdoctoral researcher in Lu’s group is the first author, Prof. Lu is the corresponding author. The other authors include Prof. Cai, huanjie and Prof. Yu, qiang from Northwest A&F University, Prof. Zhao, feng from Beihang University, and Prof. Liu, xinjie from Chinese Academy of Sciences. This work is supported by the National Natural Science Foundation of China (Grant No. 41901293, 42071328, and 41771382), the China Postdoctoral Science Foundation (Grant No. 2019M663828), and the Chinese Universities Scientific Fund (24520212452021125).
Paper link：https://www.sciencedirect.com/science/article/pii/S0034425722000074