Growth,biomass allocation,and water use efficiency of 31 apple cultivars grown under two water regimes

Plant growth, biomass allocation, carbon isotope composition (δ¹³C), and water use efficiency (WUE) of 31 cultivars of apple (Malus domestica Borkh.) grown under two water regimes were measured. Drought-stressed plants showed significant declines in tree height, trunk diameter, biomass production, and total leaf area, the extent to which depended upon cultivar. Also, gas exchange rates, instantaneous and long-term efficiencies (WUE_I and WUE_L, respectively), and values for δ¹³C differed among cultivars and watering regimes. Variations in WUE_I were mainly due to changes in stomatal conductance (g _s) under drought condition. ‘Qinguan’ and ‘Golden Delicious’ had greater trunk diameter, tree height, and had higher biomass production and WUE_L under drought stress, implying that they are more suitable for arid and semi-arid regions. Moreover, WUE_L was significantly and positively correlated with δ¹³C under two watering regimes, which suggests a potential for evaluating water use efficiency of Malus by measuring carbon isotope composition.