Modeling CO2 exchange and meteorological factors of an apple orchard using partial least square regression

The eddy covariance (EC) technique was used to measure variations of orchard-atmosphere CO2 exchange, as a function of meteorological variables in an apple orchard in 2016–2017. The annual average CO2 exchange rate was 2.295 kg m−2. Excavations and biomass assessments demonstrated that the orchard stored close to 20.6 tC ha−1 as plant C over a 15-year period. Seasonally, high rates of CO2 uptake and low CO2 emissions occurred between May and August and December and March, respectively. The maximum rates of monthly CO2 exchange were 144.44 and 153.61 gC m−2 month−1 in August 2016 and June 2017, respectively. Partial least squares (PLS) regressions were used to analyze the influence of meteorological factors to on CO2 exchange rates. Temperature and photosynthetic active radiation (PAR) were observed to exert the largest influence on driving variation in CO2 exchange. The main meteorological factors affecting CO2 exchange on daily and monthly time scales were soil temperature (Tsoil), air temperature (Ta), PAR, below canopy CO2 concentration (BCC), vapor pressure deficit (VPD), and soil water content at 50 cm (SWC50cm). The regression model equation describing CO2 exchange included Ta, VPD, precipitation (PPT), and sunshine duration (SD), as significant variables. This model curve fitting explains over 80% of the variation in CO2 exchange. This study provides CO2 exchange characteristics and a model equation capable of predicting CO2 exchange of an apple orchard.