Remotely sensed solar-induced fluorescence (SIF) has emerged as a novel approach for terrestrial vegetation monitoring. The in situ continuous optical remote sensing tool in conjunction with concurrent eddy covariance (EC) flux measurements provides a new opportunity to advance terrestrial ecosystem science. Here we introduce a network of ground-based SIF observations at flux tower sites across the mainland China referred as ChinaSpec. Until now, it consists of 15 tower sites including 5 cropland sites, 4 grassland sites, 4 forest sites and 2 wetland sites. At each of these sites, an automated spectroscopy system was deployed to collect continuous super-high resolution spectra for high-frequency SIF retrievals in synergy with EC flux measurements. The goal of ChinaSpec is to provide ground SIF measurements and promote the collaborations between optical remote sensing and EC flux communities in China. We present here the details of instrument specifications, data collection and processing procedures, data sharing and utilization protocols, and future plans. Furthermore, we show the examples how ground SIF observations can be used to track vegetation photosynthesis from diurnal to seasonal scales, to assist in the validation of fluorescence models and satellite SIF products (e.g., from OCO-2, TanSat and TROPOMI) with the measurements from these sites since 2016. This network of SIF observations could improve our understanding of the controls on the biosphere-atmosphere carbon exchange and enable the improvement of carbon flux predictions. This SIF network will also help integrate ground SIF measurements with EC flux networks which will advance ecosystem and carbon cycle researches globally.

Remotely sensed solar-induced fluorescence (SIF) has emerged as a novel and powerful approach for terrestrial vegetation monitoring. Continuous measurements of SIF in synergy with concurrent eddy covariance (EC) flux measurements can provide a new opportunity to advance terrestrial ecosystem science. Here we introduce a network of ground-based continuous SIF observations at flux tower sites across the mainland China referred to as ChinaSpec. The network consists of sixteen tower sites including 6 cropland sites, 4 grassland sites, 4 forest sites and 2 wetland sites. An automated SIF system was deployed at each of these sites to collect continuous high resolution spectra for high-frequency SIF retrievals in synergy with EC flux measurements. The goal of ChinaSpec is to provide long-term ground-based SIF measurements and promote the collaborations between optical remote sensing and EC flux observation communities in China. We present here the details of instrument specifications, data collection and processing procedures, data sharing and utilization protocols, and future plans. Furthermore, we show the examples how ground-based SIF observations can be used to track vegetation photosynthesis from diurnal to seasonal scales, and to assist in the validation of fluorescence models and satellite SIF products (e.g., from OCO-2 and TROPOMI) with the measurements from these sites since 2016. This network of SIF observations could improve our understanding of the controls on the biosphere-atmosphere carbon exchange and enable the improvement of carbon flux predictions. It will also help integrate ground-based SIF measurements with EC flux networks which will advance ecosystem and carbon cycle researches globally.

Solar-induced chlorophyll fluorescence (SIF) has been used to estimate leaf-level net CO 2 assimilation by a mechanistic light reaction (MLR-SIF) equation. However, the application of this model would be limited by the challenging measurement and estimation of input parameters (e.g. fraction of open PSII reaction centres, q L). We modified the MLR-SIF model by replacing q L by the easily obtained parameters (non-photochemical quenching [NPQ]) to facilitate its application. We employed synchronous measurements of gas exchanges, ChlF parameters and SIF for Leymus chinensis, Populus tomentosa Carrières and Ulmus pumila var. sabulosa under the soil–water deficit and rehydration process to test the robustness of the modified MLR-SIF model. Our results demonstrated that for L. chinensis the net photosynthesis rate dynamics under severe soil–water stress and saturated water condition were effectively captured by the modified MLR-SIF model ( R 2 = 0.75–0.92, RMSE = 1.11–3.56) . For P. tomentosa Carrières and U. pumila var. sabulosa, the net photosynthesis rates were predicted by the modified MLR-SIF model with good accuracy ( R 2 = 0.86, RMSE = 9.44; R 2 = 0.88, RMSE = 4.16) across the water deficit and rehydration condition . However, the electron transport rate estimated by the modified MLR-SIF model uncoupled with the photosynthetic capacity ( r 2 = -0.13) and lowered the net photosynthesis rate simulation precision ( R 2 = 0.35, RMSE = 3.41) for L. chinensis under mild drought stress and saturated light intensities. The electron transport rate estimated by the modified MLR-SIF model downregulated the photosynthetic capacity for P. tomentosa Carrières ( r 2 = 0.32) and U. pumila var. sabulosa ( r 2 = 0.22) under mild drought stress. The shift of the Rubisco and RUBP limited state cross-points, the dynamic photosynthesis parameters across the plant species and the alternative electron sinks under soil–water deficit and rehydration process influenced the simulation precision of the modified MLR-SIF model. Our modified MLR-SIF model provided a basis for understanding and inferring the photosynthetic rate by SIF and NPQ under water stress.