胡杨液流对地下水埋深变化的响应

以塔里木河流域荒漠河岸林主要建群种胡杨(Populus euphratica)为研究对象,结合中下游不同断面地下水埋深和胡杨液流变化的监测数据,分析了胡杨茎干液流与地下水埋深变化的关系,探讨荒漠环境下天然胡杨生长的合理生态水位。研究表明,胡杨液流通量密度随地下水埋深即干旱胁迫程度的加大而减小,两者呈极显著负相关,相关系数达–0.887;胡杨液流通量在地下水埋深位于4.5–5m时出现异常变化,表明此时胡杨的正常生长受到胁迫,胡杨通过自身调节降低蒸腾耗水以适应环境;土壤盐分不是影响塔里木河中下游各断面胡杨液流变化的主要因子;对植物样地调查结果分析显示,胡杨盖度、密度和频度均在地下水埋深在4–6m梯度下开始表现为降低趋势。综合分析认为维系塔里木河中下游天然胡杨正常生长的生态水位为地下水埋深4.5m以内。

Response of sap flow in Populus euphratica to changes in groundwater depth in the middle and lower reaches of the Tarim River of northwestern China

Aims Our aims were to analyze the relationship between sap flow in Populus euphratica and groundwater depth,and to determine the groundwater depth that can maintain growth in P. euphratica. Methods Sap flow flux densities of stems of P. euphratica growing in the middle and lower reachs of the Tarim River were measured using stem heat pulse techniques in August 2008. Meteorological factors were monitored by a recording weather station. Groundwater depth data were collected from monitoring wells by the conductance method. Important findings Sap flow flux density decreased with increased groundwater depth (correlation coefficient = –0.887). When the groundwater depth dropped to 4.5–5 m, sap flow flux density in P. euphratica was abnormal. Soil salt was not the main factor influencing sap flow in P. euphratica. Data collected from 74 vegetation plots show that cover, density and frequency decrease when the groundwater depth dropped to 4–6 m. We conclude that in order to restore P. euphratica and its ecosystem in the middle and lower reaches of the Tarim River, the groundwater depth must be kept at a minimum of 4.5 m.