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.

Woody plantations play a curtail role in ecological security along coastal zones. Understanding of energy partitioning and evapotranspiration (ET) over black locust plantations can reveal land-atmosphere interaction process and help us to optimize this plantation for land management in the Yellow River Delta. In this study, we investigated energy fluxes, ET in particular, and their related biophysical factors using eddy covariance techniques over a black locust plantation in 2016, 2018, and 2019. Downward longwave radiation offsets 84%–85% of upward longwave radiation, upward shortwave radiation accounted for 12%–13% of downward shortwave radiation, and the ratio of net radiation (Rn) to downward radiation was 18%–19%in the three years. During growing seasons, latent heat flux was the largest components among radiation balance terms; during non-growing seasons, sensible heat flux was a dominant component. ET was mainly controlled by Rn, air temperature, vapor pressure deficit and leaf area index (LAI). Annual ET was smaller than the sum of precipitation and irrigation, and cumulative ET was larger than cumulative precipitation during non-growing seasons. The phenology of black locust influenced the seasonal variation in daily ET, mainly via LAI. ET was larger under sea wind than under land wind, mainly because soil water content at 10-cm depth was greater under sea wind in daytime. Seasonal patterns of daily evaporative fraction, Bowen ratio, crop coefficient, Priestley–Taylor coefficient, surface conductance (gs), and decoupling coefficient were mainly controlled by LAI, and the threshold value of daily gs was approximately 8 mm s−1 over the studied plantation.