Abstract:

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.

Key words: heat balance techniques, Caragana microphylla, individual stem transpiration, leaf area, scaling-up, community transpiration