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