Characteristics of the water-energy-carbon fluxes of irrigated pear (Pyrus bretschneideri Rehd) orchards in the North China Plain

Pear trees (Pyrus bretschneideri Rehd) play an important role in the fruit production in the North China Plain (NCP) where water shortage is a serious problem. The objectives of this research were to explore the characteristics of water balance, energy transfer and carbon exchange of irrigated pear orchards by a combination of multiple measurement methods (eddy covariance system, sap flow method, and the other equipment). Experiments from 08/01/2011 to 10/31/2012 were conducted in a pear orchard located in the NCP. Annual net radiation (Rn) was 2490 MJ m−2 of which latent heat flux accounted for 74.5%, a little higher than the agro-ecosystem with wheat-maize rotation (70%). Annual mean water use efficient (WUE) was 1.98 g CO2/kg H2O which was lower than the agro-ecosystem in the same area. Annual evapotranspiration (ET) was 759 mm and daily transpiration (T) ranged from 0.5 to 4.3 mm during May to October while daily T/ET varied from 0.6 to 0.9. Variation of ET can be explained well by the change of LAI. As annual drainage was 86 mm, it will take a long time for the shallow soil water (0-140 cm) to replenish deep groundwater. Optimal values of daily downward short wave radiation (Rs) (20 MJ m−2 d−1) and ET (∼4.8 mm d−1) were probably important thresholds for the plant growth. Changing irrigation method and crops planting structure adjusting according to the water balance and trees growth characteristics, were probably useful for keeping high yield with less water depletion while further research should be done in future.