Water use efficiency and its influencing factors of Platycladus orientalis plantation in Beijing mountains area, China.

Water use efficiency (WUE) is an important index to evaluate plant drought resistance. Studying the dynamics of WUE and its influencing factors can provide reference for the vegetation restoration in Beijing mountainous area. We measured WUE of Platycladus orientalis in growing season and investigated the influence of meteorological factors, soil factors, and atmospheric CO ₂ concentration on WUE, based on the stable carbon isotope techniques. The results showed that: 1) The short-term WUE decreased and then increased in the growing season, with minimum value (2.69 mmol·mol ^-1 ) in July and maximum value (13.88 mmol·mol ^-1 ) in October. 2) The vapor pressure deficit (VPD) had the most significant impacts on WUE, followed by air temperature (T _a ), soil moisture (M _s ), relative humidity (RH), and atmospheric CO ₂ concentration (C _a ), explaining 89.7% of the total variance. Solar radiation (R _a ) and wind speed (W _s ) had no impacts on WUE. 3) VPD and T _a are the most two important factors influencing short-term WUE, explaining 53.9% of the total variance. The effects of VPD on short-term WUE was higher than that of T _a . M _s and RH were the second important factors of the short-term WUE, explaining 25.4% of the total variance. The effects of M _s on short-term WUE was higher than that of RH. C _a had little effect on the short-term WUE and could explain 10.3% of the total variance.