[Simulation of δ 18 O in Platycladus orientalis leaf water with different kinetic fractionation coefficients].

Clarifying ¹⁸ O isotope composition of leaf water (δ _L,b ) would provide theoretical refe-rence for the study of leaf physiology and forest hydrology. We continuously monitored the concentration of atmospheric water vapor (W _a ) and ¹⁸ O isotope composition of atmospheric water vapor (δ _v ) at the canopy of Platycladus lateralis plantation in the mountain area of Beijing. We analyzed the effects of kinetic fractionation coefficients Δ _k1 (32%) and Δ _k2 (28%) on the prediction of δ _L,b by combining the measured leaf water ¹⁸ O isotope (δ _x ) and δ _L,b of P. lateralis. The results showed that the diurnal variation of W _a was irregular. Atmospheric relative humidity (RH) showed a "V" shape of diurnal variation, and stomatal conductance (g _s ) increased first and then decreased at the diurnal scale. W _a , RH, and g _s showed a significant negative correlation with δ _L,b when isotopes approached a steady-state equilibrium around noon. The kinetic fractionation coefficient Δ _k1 and Δ _k2 were applied to the Craig-Gordon model to predict δ _L,b under the isotopic quasi-steady-state condition. The results showed that the predicted values of Δ _k2 approached the observed values of δ _L,b . This result indicated that the application of Δ _k2 to the model was more consistent with the change of water isotope concentration in the leaves of P. lateralis in the mountain area of Beijing. These results would improve our understanding of water isotope enrichment model and evapotranspiration resolution model in leaves.