Breeding Productive Tree Genotypes: The Role of Hydraulic Resistance Along the Root‐Stem‐Leaf Continuum in Constraining Growth

ABSTRACT Breeding productive tree genotypes is crucial for sustainable forestry, yet the hydraulic architecture along root‐stem‐leaf continuum that constrains biomass yield remains unclear. Here, six poplar hybrid genotypes with contrasting yield were used to quantify whole‐plant hydraulic resistance, its partitioning patterns, and anatomical traits along the continuum. We observed substantial genetic variations in hydraulic resistance parameters. Roots contributed the largest proportion of whole‐plant hydraulic resistance (> 54%). Components along the continuum were well‐coordinated, and hydraulic resistance of all components was strongly correlated with yield ( R 2 > 0.75), suggesting that hydraulic resistance is a strong predictor of yield. However, resistance partitioning patterns generally showed weak correlations with yield, with more productive genotypes partitioning a smaller proportion of resistance to leaves. Vessel diameter was a key determinant of hydraulic resistance at the root and leaf levels ( R 2 ≥ 0.75), and vessel length significantly influenced stem hydraulic resistance ( R 2 = 0.80). Additionally, genotypes with higher minor vein density and a lower ratio of palisade to spongy mesophyll thickness exhibited lower leaf resistance. Our results suggest that low hydraulic resistance throughout root‐stem‐leaf continuum is the functional basis for high yield, and the identification of key hydraulic and structural constraints will help overcome bottlenecks in breeding productive tree genotypes.