Xylem conduit diameter widens from leaf tip to stem base and how this widening affects the total hydraulic resistance (R_TOT) and the gradient of water potential (Ψxyl) has never been thoroughly investigated.

Data of conduit diameter of Acer pseudoplatanus, Fagus sylvatica and Picea abies were used to model the axial variation of R_TOT and Ψxyl.

The majority of R_TOT (from 79 to 98%) was predicted to be confined within the leaf/needle. This means that the xylem conduits of stem and roots, accounting for nearly the total length of the hydraulic path, theoretically provide a nearly negligible contribution to R_TOT. Consequently, a steep gradient of water potentials was predicted to develop within the leaf/needle base, whereas lower in the stem water potentials approximate those of rootlets.

Our results would suggest that the strong partitioning of R_TOT between leaves/needles coupled with basal conduit widening is of key importance for both hydraulic safety against drought-induced embolism formation and efficiency, as it minimizes the exposure of stem xylem to high tensions and makes the total plant’s conductance substantially independent of body size.

木质部导管的直径从叶尖到茎基部变宽，并且这种变宽如何影响总的水力阻力（R _TOT）和水势梯度（Ψxyl）尚未被彻底研究。

用Acer pseudoplatanus，Fagus sylvatica和Picea abies的导管直径数据来模拟R _TOT和Ψxyl的轴向变化。

R _TOT的大部分（从79％到98％）预计被限制在叶/针中。这意味着茎和根的木质部导管几乎占液压路径的总长度，理论上对R _TOT的贡献几乎可以忽略。因此，预计在叶/针基部内会形成陡峭的水势梯度，而茎中较低的水势近似于小根。

我们的研究结果表明，R / _TOT在叶/针之间的强力分配以及基管的扩宽对于防止干旱引起的栓塞形成的水力安全和效率均至关重要，因为它可以最大程度地减少茎木质部在高张力下的暴露并使整个植物的电导率基本上与体型无关。