Model li190sb

Carbon flux was measured by the eddy covariance system with a 3-D sonic anemometer (Model CSAT3, Campbell Scientific Inc., USA) and an open-path and fast response infrared CO₂/H₂O analyzer (Model Li-7500, Li-COR Inc., USA) at the height of 30 m above the surface. Raw data were collected at a frequency of 10 Hz, and the flux data were recorded by a data logger (Model CR5000, Campbell Scientific Inc., USA).
Air temperature and humidity were monitored by psychrometers (Model HMP45C, Campbell Scientific Inc., USA). A Global solar radiometer (Model CM11, Kipp and Zonen Inc., NL) was installed at the 27 m height. PAR was measured by a quantum sensor (Model LI190SB, Li-COR Inc., USA). Direct solar radiation has been monitored by a radiometer (Model CSD3, Kipp and Zonen Inc., NL) since 2016. Soil moisture at the depths of 0, 5, 10 and 20 cm was monitored by time domain reflectometry (TDR) probes (Model CS615-L, Campbell Scientific Inc., USA). Soil temperature sensors were placed at the depths of 5, 10 and 20 cm. Additionally, precipitation was measured. All above data were sampled by the data loggers (Model CR10XT and CR23XTD, Campbell Scientific Inc., USA) at 5-min intervals. Observed data from the 2011 to 2017 growing seasons has been used, except for 2015.

Routine meteorological factors, including photosynthetically active radiation (Model LI-190SB, Li-Cor Inc., Lincoln, NE, USA), air temperature (Model HMP45C, Vaisala, Helsinki, Finland), precipitation (Model 52203, Young Co., Traverse City, MI, USA), and soil water content (Model CS616, Campbell Scientific, Logan, UT, USA). The depth of measuring surface soil temperature was 5 cm. The daily, 8 days and monthly average SIF were also calculated. Due to the malfunction of sensor, soil water content during January to March was abnormal and was excluded in the analysis.