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We explored the relationship between tree growth, water use, and related hydraulic traits in <i>Populus deltoides</i> Bartr. ex Marsh.and hybrid clones, to examine potential trade-offs between growth and water use efficiency. Nine genotypes, six <i>P. deltoides</i> and three hybrid clones, that represented genotypes with high (Group H), intermediate (Group I), and low (Group L) growth performance were selected for study, based on year-two standing stem biomass in a replicated field trial. In year four, tree growth, transpiration (<i>E</i>_t), canopy stomatal conductance (<i>G</i>_s), whole-tree hydraulic conductance (<i>G</i>p), and carbon isotope discrimination (<i>&#916;</i>¹³C) were measured. Tree sap flux was measured continuously using thermal dissipation probes. We hypothesized that Group H genotypes would have increased growth efficiency (GE), increased water use efficiency of production (WUEp, woody biomass growth/<i>E</i>_t), lower <i>&#916;</i>¹³C, and greater <i>G</i>p than slower growing genotypes. Tree GE increased with relative growth rate (RGR), and mean GE in Group H was significantly greater than L, but not I. Tree WUEp ranged between 1.7 and 3.9 kg biomass m³ H₂O^&#8722;¹, which increased with RGR. At similar levels of <i>E</i>_t, WUEp was significantly greater in Group H (2.45 &#177; 0.20 kg m^&#8722;³), compared to I (2.03 &#177; 0.18 kg m^&#8722;³) or L (1.72 &#177; 0.23 kg m^&#8722;³). Leaf and wood <i>&#916;</i>¹³C scaled positively with stem biomass growth but was not correlated with WUEp. However, at a similar biomass increment, clones in Group H and I had significantly lower leaf <i>&#916;</i>¹³C than Group L. Similarly, Group H clones had a significantly lower wood <i>&#916;</i>¹³C than Group L, supporting our hypothesis of increased WUE in larger trees. Tree physiological and hydraulic traits partially explain differences in WUEp and <i>&#916;</i>¹³C, and suggest that clone selection and management activities that increase tree biomass production will likely increase tree and stand WUE. However, more research is needed to discern the underlying hydraulic mechanisms responsible for the higher WUE exhibited by large trees and distinct clones.