Relationship between stable carbon isotope discrimination and water use efficiency under regulated deficit irrigation of pear-jujube tree

To investigate the relationship between stable carbon isotope discrimination (Delta) of different organs and water use efficiency (WUE) under different water deficit levels, severe, moderate and low water deficit levels were treated at bud burst to leafing, flowering to fruit set, fruit growth and fruit maturation stages of field grown pear-jujube tree, and leaf stable carbon isotope discrimination (Delta(L)) at different growth stages and fruit stable carbon isotope discrimination (Delta(F)) at fruit maturation stage were measured. The results indicated that water deficit had significant effect on Delta(L) at different growth stages and Delta(F) at fruit maturation stage. As compared with full irrigation, the average Delta(L) at different growth stages and Delta(F) at fruit maturation stage were decreased by 1.23% and 2.67% for different water deficit levels, respectively. Delta(L) and Delta(F) among different water deficit treatments had significant difference at the same growth stage (P < 0.05). Under different water deficit conditions, significant relationships between the Delta(L) and WUEi (photosynthesis rate/transpiration rate, P-n/T-r), WUEn (photosynthesis rate/stomatal conductance of CO2. P-n/g(s)), WUEy (yield/crop water consumption, Y/ETc and yield, or between the Delta(F) and WUEy and yield were found, respectively. There were significantly negative correlations of Delta(L) with WUEi, WUEn, WUEy and yield (P < 0.01) at the fruit maturation stage, or Delta(L) with WUEi and WUEn (P < 0.01) over whole growth stage, respectively. Delta(F) was negatively correlated with WUEy, WUEn and yield (P < 0.05), but positively correlated with ETc (P < 0.01) over the whole growth stage. Thus Delta(L) or Delta(F) can compare WUEn and WUEY, so the stable carbon isotope discrimination method can be applied to evaluate the water use efficiency of pear-jujube tree under the regulated deficit irrigation. (C) 2009 Elsevier B.V. All rights reserved.