小叶锦鸡儿灌丛群落蒸腾耗水量估算方法

ESTIMATION OF TRANSPIRATION IN COMMUNITIES DOMINATED BY SHRUB CARAGANA MICROPHYLLA

为了确定沙地小叶锦鸡儿(Caragana microphylla)人工林的蒸腾速率,于2006年6月运用热平衡茎流测量技术,对科尔沁沙地一处15a生人工小叶锦鸡儿群落的分枝液流动态进行了监测。根据生物统计结果选取被测标准枝,标准枝基径在0.4～1cm范围内。同时,分别用基径总断面积推算法和叶片密度推算法对灌丛叶面积进行了估算。以叶面积为扩展纯量,利用标准枝液流对灌丛群落耗水量进行尺度转换,在转换过程中,假设叶面积与蒸腾耗水量之间具有很强的相关性。该尺度转换方法经与大型称重式Lysimeter测值对比验证,误差小于14.3%,可望准确估算小叶锦鸡儿灌丛群落的蒸腾耗水量。

Aims Our objectives were to develop an appropriate procedure for scaling up the sap flow from individual stems to the whole shrub and to the plot and to assess the utility of using sap flow gauges to determine the stand-level transpiration of shrub plantations in a semiarid sandy environment. Methods Sap flow rates of stems in a 15-year-old Caragana microphylla shrub in Horqin Sandy Land, China were measured using the stem heat balance techniques in June 2006 to determine transpiration of the C. microphylla plantation. The gauge-equipped stems, ranging in basal diameter from 0.4 to 1 cm, were selected on the basis of statistical analysis within the representative sampling plot for determining the ＂mean stem＂. Synchronously, total leaf area of the plant was measured by the basal cross-sectional area method and the leaf area density （LAD） method. We took advantage of the sparse distribution of C. microphylla and the ease of directly measuring LAD for individual shrubs to create a new scaling method based on these direct LAD measurements for shrubs in the study plot. We extrapolated the measurements of water use by individual stems to determine the area-averaged transpiration of the shrubland. The method used for the extrapolation assumed that the transpiration of a shrub was proportional to its leaf area. Important findings We found daily differences of 〈14.3% between transpiration estimated with sap measurements and with a weighing lysimeter reference, suggesting that the scaling procedure can be used to provide reliable estimates of transpiration from the shrub C. microphylla in Horqin Sandy Land.