Abstract
The information on transpiration is vital for sustaining fragile ecosystem in arid/semiarid environment, including the Horqin Sandy Land (HSL) located in northeast China. However, such information is scarce in existing literature. The objectives of this study were to: (1) measure sap flow of selected individual stems of two sand-fixing plants, namely Salix gordejevii and Caragana microphylla, in HSL; and (2) upscale the measured stem-level sap flow for estimating the community-level transpiration. The measurements were done from 1 May to 30 September 2015 (i.e., during the growing season). The upscaling function was developed to have one dependent variable, namely sap flow rate, and two independent variables, namely stem cross-sectional area of Salix gordejevii and leaf area of Caragana microphylla. The results indicated that during the growing season, the total actual transpiration of the Salix gordejevii and Caragana microphylla communities was found to be 287 ± 31 and 197 ± 24 mm, respectively, implying that the Salix gordejevii community might consume 1.5 times more water than the Caragana microphylla community. For this same growing season, based on the Penman–Monteith equation, the total actual evapotranspiration for these two communities was estimated to be 323 and 229 mm, respectively. The daily transpiration from the upscaling function was well correlated with the daily evapotranspiration by the Penman–Monteith equation (coefficient of determination R2 ≥ 0.67), indicating the applicability of this upscaling function, a useful tool for managing and restoring sand-fixing vegetations.
Highlights
Like other arid/semiarid regions across the world, northeast China is incurring various levels of desertification, which can impact about 2.62 × 106 km2 land (i.e., 27.3% of the territory ofChina) [1]
Commercial probes are available that are designed to measure sap flow based on the thermal balance method, and they have been shown to be appropriate for brush branches with a small diameter [15,16,17]
The leaf area varies from subplot to subplot or from one shrub to another
Summary
Like other arid/semiarid regions across the world, northeast China is incurring various levels of desertification, which can impact about 2.62 × 106 km land (i.e., 27.3% of the territory ofChina) [1]. The shrubs play important roles in sustaining the fragile ecosystem by providing a habitant shelter from strong wind, stabilizing sand dunes, conserving soil water, and maintaining the regional ecological balance [3]. For such desert lands, because the hydrological processes are dominated by vertical soil moisture movement, it is needed to accurately determine the evapotranspiration [4]. The traditional experimental methods, such as isotopic tracers [6], potting and weighing [7], lysimeters [8], photosynthesis systems [9], and porometers [10], usually malfunction in directly measuring the transpiration of sparse vegetation in arid/semiarid environment, while the existing mathematical formulas were not developed for such situations and have very poor estimation accuracy [11]. Commercial probes are available that are designed to measure sap flow based on the thermal balance method, and they have been shown to be appropriate for brush branches with a small diameter [15,16,17]
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