Sap flow of irrigated Populus alba var. pyramidalis and its relationship with environmental factors and leaf area index in an arid region of Northwest China

Abstract

Populus alba L. var. pyramidalis Bge. (Populus) is a main tree of the farmland shelter-belt system in the arid region of Northwest China. However, soil moisture cannot satisfy the water requirements of normal Populus growth under local natural conditions, thus studying the transpiration characteristics of irrigated Populus and its relationship with the environmental factors and growth parameters is very important to the growth of the trees in this region. In this study, the sap flow of two irrigated Populus trees was measured during May to September from 2005 to 2008 using the heat-pulse technique. The results show that the maximum and minimum daily sap fluxes in Populus were 15.7-24.0 and 3.0-4.0 L day -1 , respectively. And the sum of sap fluxes from June to August accounted for approximately 63-69% of the total sap flux during May to September (almost the whole growing season). The order of the meteorological factors affecting the daily sap flux of Populus was: vapor pressure deficit [ solar radiation [ mean air temperature [ wind speed. Furthermore, a highly linear relationship between the ratio of daily sap flux to the reference evapotranspiration (SF/ET 0 ) and the amount of soil water in the 0-2.0 m layer was found, indicating that the amount of soil water at this layer was quite important to the growth of Populus in this region. Especially, the amount of soil water in the 0.5-1.0 m soil layer contributed to most of the plant transpiration as the highest coefficient of determination at this layer. Based on the environmental factors and leaf area index influencing sap flux, an empirical transpiration model was constructed to estimate daily transpiration.

Environmental and physiological controls on sap flow in a subhumid mountainous catchment in North China

“…This indicates that the impact of LAI on SFD was a dominant control during this tree physiological period. This result is similar to the results of several other studies conducted on perennial deciduous plants (Chen et al, 2014;Gong et al, 2005;Granier et al, 2000;Liu et al, 2012;Ma et al, 2012;Oren and Pataki, 2001;Wullschleger et al, 2001;Xu et al, 2011;Zeppel and Eamus, 2008).…”

“…The correlation of sap flow to radiation was pronouncedly closer than that to air temperature and vapor pressure deficit, and this finding is consistent with a study conducted in Qinghai spruce (Picea crassifolia) in the upper Heihe River Basin of arid northwestern China (Chang et al, 2014). However, sap flow showed a much stronger relationship with radiation (with much higher R 2 ) in this study when compared with other studies (Chang et al, 2014;Chen et al, 2014;Oren and Pataki, 2001;Xu et al, 2011). The linear correlations of the two integrated meteorological indicators, VT and ET 0 , with SFD were quite significant, as they explained 61.62% and 71.89% of the variation in SFD, respectively (see Fig.…”

“…Soil moisture content reflects soil water availability for tree transpiration. Several studies conducted in arid and semi-arid regions have suggested a positive relation between sap flow and soil moisture (Chang et al, 2014;Chen et al, 2014;Huang et al, 2010;Liu et al, 2012;Nicolas et al, 2005;Small and McConnell, 2008;Xu et al, 2011). Du et al (2011) noted that the influences of environmental factors on sap flow vary with tree species, growth status, hydroclimatic characteristics, bedrock properties, edaphic features, etc.…”

“…Evaporative demand, available energy, and water availability can be reflected by environmental factors. Previous studies have indicated that vapor pressure deficit, radiation, and air temperature are the most important environmental factors controlling sap flow, especially vapor pressure deficit and radiation (Chang et al, 2014;Chen et al, 2014;Du et al, 2011;Liu et al, 2012;Nagler et al, 2003;Phillips et al, 1999;Xu et al, 2011). Vapor pressure deficit reflects the level of atmospheric evaporative demand for water vapor, and radiation provides the available energy for sap flow.…”

“…These studies revealed that the major controlling factors of sap flow include, but are not limited to, vapor pressure deficit, radiation, air temperature, soil moisture, and leaf area index, while the environmental and physiological controls on sap flow vary significantly with environmental/hydro-climatic conditions, tree species and time period. Several studies have combined environmental factors with physiological factors to acquire more-accurate estimates of sap flow (Chang et al, 2014;Chen et al, 2014;Liu et al, 2012;Wullschleger et al, 2001;Xu et al, 2011), while the forms of the estimates are quite different from each other.…”