中国沙棘根尖功能特征对坡位和动物啃食枝叶的响应

揭示中国沙棘（Hippophae rhamnoides subsp.sinensis Rousi）根尖在形态、水力结构和非结构性碳水化合物（NSC）浓度对环境条件及外界干扰的响应有利于全面了解中国沙棘对环境条件在水分利用和碳素分配上的适应能力和适应策略。以山西省交城县野生沙棘林为研究对象，选取坡下部正常、坡下部动物啃食、坡上部正常和坡上部动物啃食4种类型沙棘，分析沙棘根尖形态、水力结构、非结构性碳水化合物（NSC）的响应。结果显示：与坡下部相比，在坡上部相对缺水的环境下中国沙棘根尖比根长显著增加，根尖的平均长度、直径、皮层厚度和中柱直径没有显著性变化，根尖导管直径降低、导管密度增加；根尖的比导水率正常和动物啃食分别降低18.12%和20.6%，水力脆弱性指数分别降低45.40%和48.5%，NSC含量没有显著性变化。动物啃食导致根尖比根长降低、平均直径增加、皮层厚度和中柱直径增加，导管直径降低、导管密度增加，坡上和坡下动物啃食导致比导水率降低71.14%和70.25%，水力脆弱性指数降低23.95%和19.41%。以上结果表明：坡上部较差的水分条件使中国沙棘根尖有更大的吸收面积，水分输导效率小幅降低，水力安全性较大程度提升；动物啃食导致根尖增粗、导水率较大程度降低、水力安全性小幅提升。坡位和动物啃食均未导致根尖NSC含量降低，动物啃食在坡上部相对缺水的环境中根尖响应程度更大。这表明中国沙棘根尖对坡位和动物啃食的响应有助于对两种影响因素的适应，动物啃食对根尖吸收和运输功能的影响程度更大。

Response of root tip function characteristics of Hippophae rhamnoides subsp. sinensis Rousi to slope position and herbivores grazing on branches and leaves

Revealing the response of the root tip in morphology, hydraulic structure and non-structural carbohydrate (NSC) concentration to environmental conditions and external disturbances is conducive to comprehensive understanding of the adaptive capacity and adaptive strategies of sea-buckthorn (Hippophae rhamnoides subsp. sinensis Rousi). This study was conducted on four wild sea-buckthorn forest types in Jiaocheng, Shanxi, growing in upper and lower slope with or without herbivores grazing to analyzed the response of root tip morphology, hydraulic structure and non-structural carbohydrate. Results showed that compared with those growing in the lower part of the slope, the specific root length of root tip and the density of root tip vessels of sea-buckthorn trees under the environment of relative water shortage on the upper slope increased significantly, and the diameter of root tip vessels decreased significantly. Meanwhile the mean length, mean diameter, cortical thickness and diameter of the central column of the root tip did not change significantly, and the specific hydraulic conductivity of root tip with and without herbivores grazing decreased by 18.12% and 20.6%, the hydraulic vulnerability index by 45.40% and 48.5%, respectively. However, the root tip NSC content did not change significantly. Herbivores grazing led to the decrease of the specific root length of root tip, the increase of the root tip mean diameter, cortical thickness and diameter of the central column, similarly decreased the diameter of root tip vessels and increased the density of root tip vessels. Herbivores grazing also led to the specific hydraulic conductivity of root tip decreased by 71.14% and 70.25%, and the hydraulic vulnerability index decreased by 23.95% and 19.41% for sea-buckthorn trees at the upper and the lower slope, respectively. The above results suggested that the poor water condition in the upper slope could make the root tip of sea-buckthorn trees have larger absorption area, a little lower water transport efficiency, and greatly improved hydraulic safety. And the herbivores grazing led to the thickening of root tip, the great reduction of hydraulic conductivity, and the slight improvement of safety. The NSC content in root tip did not decrease due to the slope position or herbivores grazing. The response of root tip to herbivores grazing was greater on the upper slope. This indicates that the response of root tip of sea-buckthorn trees to slope position and herbivores grazing is helpful for them to adapt to the two influencing factors, and herbivores grazing has a greater impact on root tip absorption and transportation functions.