拉萨半干旱河谷主要植被恢复树种耗水规律及机理研究

Forest plays a huge ecological function, but it also consumes large amounts of water to maintain the normal operation of its own ecosystem. In arid and semi-arid regions of serious shortage of water resources, the water consumption of accounts for a sizeable proportion of the water balance system of the entire region. Although at home and abroad forest water consumption has been considerable researched and achieved valuable results in some areas, research about forest water consumption is not yet carried out in Tibet's special environment. Therefore, the major tree and shrub species grown in the semi-arid valley of Lhasa will be the research objects. Around the dynamic monitoring of water movement in the SPAC system, Transpiration Characteristics, physiological and ecological environmental factors, water consumption specific mechanism of of the different species will be systematic researched by means of the the potted control and field sap flow dynamics of monitoring under specific environmental conditions in the Lhasa River valley. The purpose of the research is to grasp the Transpiration Regulation and Water Consumption Mechanism about major vegetation recovery species, and to provide theoretical and technical support for the selection of tree species, stand density, species configuration, the forest coverage of scientific and rational planning and design, and regional water ecological economic management. The study of the forest water consumption mechanism specific performance of high altitude area will further explore the internal adjustment mechanism and rich forest water consumption theory.

森林在发挥巨大生态功能的同时，要消耗大量水分以维持自身生态系统正常运转，在水资源严重紧缺的干旱半干旱地区，森林耗水在整个地区水量平衡系统中占有相当大的比重。国内外对林木耗水性已有相当的研究，且在局部地区取得了比较有价值的结果，但在西藏这种特殊的环境下尚未开展有关树木耗水方面的系统研究。为此，本项目以拉萨半干旱河谷植被恢复的主要乔灌木树种为研究对象，围绕SPAC系统内水分运动的动态监测，通过盆栽控制和野外树干液流动态监测等手段，在拉萨河谷特定环境条件下对不同树种的蒸腾耗水特性、生理生态相关环境因子、耗水特异性机制等进行系统研究，以期掌握主要植被恢复树种蒸腾耗水规律及耗水机制，为该地区植被恢复中树种选择、林分密度、树种配置、森林覆盖率的科学合理规划设计及区域水分生态经济管理提供理论及技术支撑；高海拔地区林木耗水机制的特异性表现研究将进一步探索林木耗水的内在调节机制、丰富林木耗水研究理论。

在干旱和半干旱地区，水资源量的严重不足及降水时空的差异加剧了水资源的亏缺状况及林业对水的依赖程度。树木耐旱和耗水问题也越来越受到国内外相关专家及学者的关注，本研究在西藏这种特殊的环境下针对拉萨半干旱河谷主要植被恢复树种展开。在拉萨半干旱河谷特定环境条件下以3年生苗木为对象对9个主要造林树种幼苗的蒸腾耗水特性和水分利用效率进行研究，4个乔木树种均能耐受一定程度的水分亏缺，属耐旱较强的树种，综合各因素，4个树种耐旱性的排序为：榆树＞藏川杨＞左旋柳＞银白杨。各灌木树种中在干旱胁迫下耗水量较低，砂生槐的水分利用效率在正常供水条件下达到最大值6.0µmolCO2·mmol-1H2O，其在各水分胁迫下均显著高于其他树种近50%，一定的干旱胁迫有利于醉鱼草耐旱性的提高，香柏、细叶小红柳和江孜沙棘均在轻度干旱时达到最大水分利用效率，而过于湿润的土壤环境条件不利于细叶小红柳、香柏和江孜沙棘的生长。各树种在不同水分条件下的生长指标、生理生化指标及解剖结构间均存在差异，砂生槐表现出较大的特异性，其叶片POD含量均显著高于其他树种，且栅栏组织层数比其余树种多。运用Granier热扩散探针技术，在西藏拉萨半干旱河谷对藏川杨和北京杨的树干液流进行连续观测，并同步测定太阳辐射（Q）、空气温度(Ta), 饱和蒸气压亏缺 (VPD)、空气湿度、土壤含水量(SWC)等环境因子。结果显示在拉萨河谷区旱季和雨季较大气候差异的环境下，藏川杨和北京杨树干液流速率均具有较为明显的昼夜节律。但两树种树干液流在峰值、日平均值、启动时间以及受环境因子的影响方面均存在明显差异，特别是在干旱季节尤为显著，藏川杨作为乡土树种显示出更强的适应性。