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Abstract Stem growth reflects genetic and phenotypic differences within a tree species. The plant hydraulic system regulates the carbon economy, and therefore variations in growth and wood density. A whole-organism perspective, by partitioning the hydraulic system, is crucial for understanding the physical and physiological processes that coordinately mediate plant growth. The aim of this study was to determine whether the relationships and trade-offs between (i) hydraulic traits and their relative contribution to the whole-plant hydraulic system, (ii) plant water transport, (iii) CO2 assimilation, (iv) plant growth, and (v) wood density are revealed at the interclonal level within a variable population of 10 Pinus radiata (D. Don) clones for these characters. We demonstrated a strong coordination between several plant organs regarding their hydraulic efficiency. Hydraulic efficiency, gas exchange, and plant growth were intimately linked. Small reductions in stem wood density were related to a large increase in sapwood hydraulic efficiency, and thus to plant growth. However, stem growth rate was negatively related to wood density. We discuss insights explaining the relationships and trade-offs of the plant traits examined in this study. These insights provide a better understanding of the existing coordination, likely to be dependent on genetics, between the biophysical structure of wood, plant growth, hydraulic partitioning, and physiological plant functions in P. radiata. 

Stomatal regulation is crucial for forest species performance and survival on drought‐prone sites. We investigated the regulation of root and shoot hydraulics in threePinus radiataclones exposed to drought stress and its coordination with stomatal conductance (g_s) and leaf water potential (Ψ_leaf). All clones experienced a substantial decrease in root‐specific root hydraulic conductance (K_root‐r) in response to the water stress, but leaf‐specific shoot hydraulic conductance (K_shoot‐l) did not change in any of the clones. The reduction inK_root‐rcaused a decrease in leaf‐specific whole‐plant hydraulic conductance (K_plant‐l). Among clones, the larger the decrease inK_plant‐l, the more stomata closed in response to drought. Rewatering resulted in a quick recovery ofK_root‐randg_s. Our results demonstrated that the reduction inK_plant‐l, attributed to a down regulation of aquaporin activity in roots, was linked to the isohydric stomatal behaviour, resulting in a nearly constant Ψ_leafas water stress started. We concluded that higherK_plant‐lis associated with water stress resistance by sustaining a less negative Ψ_leafand delaying stomatal closure.