北京山区干旱胁迫下侧柏叶片水分吸收策略

干旱与半干旱地区，水分是限制树木生长的重要影响因子。由于降水稀缺且分配不均，叶片吸收水分是此地区树木吸收和利用小量级降水和凝结水的主要方式。北京山区处于易旱少雨的生态脆弱地带，森林植被经常遭受干旱胁迫，所以对该地区的森林系统而言，叶片直接吸收利用截留的降雨是干旱时期树木获得水分的重要途径。基于野外对比控制试验和室内盆栽模拟试验，选取北京山区的主要造林树种侧柏为研究对象，进行利用天然降雨与模拟降雨试验，研究降雨前后侧柏叶片吸水特征，探究侧柏在干旱环境下如何通过叶片吸水缓解干旱胁迫。结果表明：当侧柏长期处于干旱胁迫状态时，叶片可以利用降雨，从中获益用来缓解树木的干旱胁迫状态；叶片的吸水能力与降雨强度呈正相关关系，与土壤含水率呈负相关关系；重度干旱下侧柏植株在降雨强度为15 mm/h时叶片吸水现象最明显，叶水势变化最大为(1.18±0.17) MPa,叶片含水率变化最大为(8.47±1.00)mg/cm~2;当土壤水率高于20.8%时，基本不发生叶片吸水现象。试验结果说明在干旱地区叶片吸水是树木除根系吸水外的重要水分来源方式，并且对干旱地区有效利用短缺水资源，减轻植物水分亏缺具有重要意义。

Leaf water absorption of Platycladus orientalis under drought stress in Beijing

In arid and semi-arid areas, water is an important factor that restricts the growth of trees. Due to the scarcity and uneven distribution of precipitation, the leaf absorption of water is the main way for trees in this area to absorb and use small amounts of precipitation and condensate. The mountainous area of Beijing is located in an ecologically fragile zone prone to drought and less rain. Forest vegetation often suffers from drought stress. Therefore, for the forest system in this area, the direct absorption and use of intercepted rainfall by leaves is an important way for trees to obtain water during dry periods. Based on field comparative control experiments and indoor pot plant simulation experiments, Platycladus orientalis, the main afforestation tree species in Beijing mountainous areas, was selected as the research object. Natural rainfall and simulated rainfall experiments were carried out to study the water absorption characteristics of Platycladus orientalis leaf before and after rainfall, and explore how Platycladus orientalis under arid environment alleviate drought stress by absorbing water by leaves. The results show that when Platycladus orientalis is under drought stress for a long time, the leaves can use rainfall to alleviate the drought stress of trees; the water absorption capacity of leaves is positively correlated with rainfall intensity and negatively correlated with soil moisture content; Under severe drought, Platycladus orientalis plants have the most obvious water absorption phenomenon when the rainfall intensity is 15 mm/h. The maximum change in leaf water potential is (1.18±0.17) MPa, and the maximum change in leaf water content is (8.47±1.00) mg/cm²; When the soil moisture content is higher than 20.8%, there is basically no water absorption by the blades. The test results show that leaf water absorption in arid areas is an important source of water for trees in addition to root water absorption, and it is of great significance for effective use of scarce water resources in arid areas and alleviating plant water deficit.