Biomass accumulation, allocation, and water-use efficiency in 10 Malus rootstocks under two watering regimes

Variations in biomass productivity, plant water-use efficiency (WUEp), and carbon isotope composition (δ13C) were investigated among 10 Malus rootstocks. In the semi-controlled environmental of a greenhouse, plants were watered to either 75% or 50% of field capacity. For each treatment, significant differences were found in dry matter accumulation and allocation, δ13C, and WUEp. Relative growth rate (RGR) was correlated with WUEp but not with allocation pattern. Variations in whole-plant transpiration were a result of fluctuations in the rate of transpiration per unit leaf area rather than from differences in leaf area or root weight per plant. Values for transpiration per unit leaf area or root weight were lower when the proportion of either leaf area or root weight per unit plant weight was larger. Rootstock differences in δ13C were related to changes in stomatal conductance rather than in net photosynthesis. Finally, δ13C was significantly correlated with WUEp and rootstock rankings based on both of those parameters were maintained regardless of watering treatment.