Drought and nitrogen (N) addition have been shown to affect tree hydraulic traits, but few studies have been made on their interactions across species with different wood types or leaf forms. We examined the responses of hydraulic conductance and xylem anatomical traits of Quercus mongolica (ring porous with simple leaves), Fraxinus mandshurica (ring porous with compound leaves) and Tilia amurensis (diffuse porous with simple leaves) to drought, N addition and their interactions. Drought stress decreased current-year xylem-specific conductivity in stems (K_sx) and leaf hydraulic conductance (K_leaf ), but N addition affected K_sx and K_leaf differently among species and watering regimes. These divergent effects were associated with different responses of anatomical traits and leaf forms. Higher mean vessel diameter in stems and lower vessel density in leaves were observed with N addition. The three-way interactive effects of drought, N addition and tree species were significant for most values of anatomical traits. These results were also reflected in large differences in vessel diameter and density among species with different wood types or leaf forms. The two-way interactive effects of drought and N addition were significant on K_leaf and predawn water potential, but not K_sx, indicating that leaves were more sensitive than stems to a combination of drought stress and N addition. Our results provide mechanistic insight into the variable responses of xylem water transport to the interactions of drought and N availability.

中文翻译：

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3种温带树木应对干旱，氮增加的水力传导和茎叶解剖特征的差异。

干旱和氮（N）的添加已显示出会影响树木的水力性状，但很少有人研究它们在具有不同木材类型或叶形的物种之间的相互作用。我们研究了蒙古栎（有单叶的环状孔），水曲柳（有复叶的环状孔）和紫ilia（有单叶的分散孔）的水力传导和木质部解剖特征对干旱，氮添加及其相互作用的响应。干旱胁迫降低了当年茎的木质部比电导率（K _sx）和叶片水导率（K _leaf），但是氮的添加影响了K _sx和钾_叶在物种和浇水方式之间有所不同。这些不同的效果与解剖学特征和叶片形态的不同响应有关。添加氮肥后，茎中的平均血管直径更高，叶片中的血管密度更低。干旱，氮素添加和树木物种的三种交互作用对于大多数解剖学特征值均具有重要意义。这些结果还反映在具有不同木材类型或叶形的物种之间的容器直径和密度差异很大。干旱和N另外的双向互动效应上显著ķ_叶和黎明前水势，但不ķ _SX，表明叶片对干旱胁迫和氮添加的组合比茎更敏感。我们的研究结果为木质部水运输对干旱和氮素相互作用的可变响应提供了机械的见解。