中文摘要：

为揭示黄土高原子午岭林区植被演替过程中的水分利用特性，该研究对子午岭林区演替早期种（山杨和白桦）和演替顶级种（辽东栎）的水力结构特性，包括比导水率（Ks）、比叶导水率（K1）、Huber值（Hv）和水力脆弱性等进行了比较研究。结果表明：（1）辽东栎叶片的饱和渗透势（ψsat）、膨压损失点对应的渗透势（ψtlp）和相对含水量（RWCtlp）明显低于山杨和白桦，且有高的叶水容。（2）辽东栎的最大Ks高于山杨和白桦，但HV值低于山杨和白桦，导致3种树种的最大K1差异不大。（3）无论是叶还是枝干，辽东栎抵抗栓塞的能力均大于山杨和白桦，其水分传输安全距离（旱季叶最低水势砜。与导水率损失50％时对应的叶或枝干木质部水势ψ50之差）和叶对枝干的水力保护作用（叶与枝干的ψ50之差）也明显大于山杨和白桦。（4）2种演替早期树种山杨和白桦的水力结构特性差异不大。研究认为，黄土高原子午岭林区植被演替顶极种辽东栎耐脱水能力强、叶水容大、抵抗栓塞能力相对强以及水分传输安全性高等特性是其耐旱性强于演替早期种山杨和白桦的重要原因。

英文摘要：

To determine water use traits during vegetation succession in Ziwuling forest zone on the Loess Plateau, we selected three native deciduous tree species：Populus davidiana, Betula platyphylla （early succession species） and Quercus liaotungensis （climax succession species） from Ziwuling forest zone as the materials, and compared their hydraulic architecture traits including specific conductivity （Ks）, leaf specific conductivity （KI）, Huber value （HV） and the vulnerability to embolism,etc. The results showed that： （1） Q. liaotungensis had lower saturated osmotic potential （ψsat）,osmotic potential at turgot loss point （ψtlp）, relative water content at turgor loss point （RWCtlp） and higher leaf capacitance （Cleaf） than that of P. da- vidiana and B. platyphylla. （2）Quercus liaotungensis had higher maximum Ks and lower HV than that of early succession species P. davidiana and B. platyphylla, thus maximum KI for these three species was the same. （3）For both leaf and branch, Quercus liaotungensis was more resistant to embolism than P. davidiana and B. platyphylla, meanwhile, Q. liaotungensis also had a larger hydraulic safety margin when bal- anced by the difference of minimum leaf water potential during dry season （ψmin） and xylem water potential corresponding to 50 % loss of conductivities （ψ50）,and larger leaf hydraulic protection for branch when es- timated by the difference between leaf ψ50 and branch ψ50. （4）No hydraulic architecture difference was found for two early succession species P. davidiana and B. platyphylla. These results demonstrated from plant hydraulics that higher dehydration tolerance, larger leaf capacity, stronger leaf and branch embolism resistance,higher hydraulic safety at Q. liaotungensis may be responsible for its higher drought tolerance compared with early succession species P. davidiana and B. platyphylla.