Abstract
Reliable estimation of gross primary production (GPP) of terrestrial ecosystems is crucial in the global carbon cycle and ecosystem functioning studies. Solar-induced chlorophyll fluorescence (SIF) has emerged as an unprecedented proxy for terrestrial GPP estimation. TanSat SIF with a 2-km fine spatial resolution provides an excellent opportunity to investigate the relationships of satellite SIF and eddy covariance (EC) GPP at ecosystem or site scale, while has not been investigated. In this study, we investigated the relationship between TanSat SIF and EC GPP based on flux tower sites encompassing different biomes over the globe. TanSat SIF exhibited strong relationships with EC GPP at Fe and KI bands for instantaneous and daily timescales. The correlations between EC GPP and TanSat SIF (R2 = 0.61) were much better than moderate resolution imaging spectroradiometer (MODIS) bidirectional reflectance distribution function (BRDF)- corrected vegetation indices (VIs) (R2 = 0.480.58). Further comparisons between SIF and GPP with absorbed photosynthetically active radiation (APAR) and two environmental factors (fTmin and fVPD) showed that SIF responded to APAR and was similarly affected by environmental factors as GPP. GPP derived from SIF (R2 = 0.64) also performed slightly better than enhanced vegetation index (EVI) and near-infrared reflectance of vegetation (NIRv) and even light use efficiency MODIS GPP algorithm (R2 = 0.580.60). Therefore, our results demonstrated the feasibility of SIF on estimating GPP at sites or ecosystem levels; in addition, incorporating TanSat SIF with other satellite SIF products will open a new era for carbon cycling and ecosystem functioning studies.
Highlights
Estimating terrestrial vegetation photosynthesis is significant to understanding the global carbon cycle and monitoring ecosystem productivity [1,2,3]
We found that TanSat-derived solar-induced chlorophyll fluorescence (SIF) at both Fe and KI band well tracked the seasonal cycle of eddy covariance (EC) gross primary productivity (GPP), which indicating the potential of satellite-derived SIF on estimating GPP
In order to help evaluate the capability of TanSat SIF on estimating GPP, we examined the relationships between EC GPP and moderate resolution imaging spectroradiometer (MODIS)-derived normalized difference vegetation index (NDVI), enhanced vegetation index (EVI) and nearinfrared reflectance of vegetation (NIRv)
Summary
Estimating terrestrial vegetation photosynthesis is significant to understanding the global carbon cycle and monitoring ecosystem productivity [1,2,3]. Reflectance-based vegetation indices (VIs), such as normalized difference vegetation index (NDVI) and enhanced vegetation index (EVI), are widely used in regional and global vegetation gross primary productivity (GPP) estimation [4,5,6]. Solar-induced chlorophyll fluorescence (SIF) has been deemed as an alternative proxy for estimating terrestrial GPP due to its close link to photosynthesis [8,9,10,11]. Three different pathways are mainly included when plant chlorophyll molecules absorb light energy: nonphotochemical quenching (NPQ), photochemistry, and reemitted as SIF [12, 13]. Compared with the traditional VIs, SIF shows a close physiological correlation with the photosynthesis status of vegetation [14, 15]
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