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Analyses of transpiration water consumption of Abies georgei var. smithii and its driving factors in southeastern Tibet
LI Jiangrong, GUO Qiqiang, ZHENG Weilie
JOURNAL OF NANJING FORESTRY UNIVERSITY ›› 2021, Vol. 45 ›› Issue (6) : 151-158.
PDF(2255 KB)
PDF(2255 KB)
Analyses of transpiration water consumption of Abies georgei var. smithii and its driving factors in southeastern Tibet
【Objective】 The transpiration water consumption of Abies georgei var. smithii individuals with different diameters at breast height (DBH) was studied, and its correlations with meteorological factors were analyzed. This information could provide an important reference for understanding the forest growth rule in the sub-high mountain area of Tibet Autonomous Region. 【Method】 A stem sap flow measurement system was used to measure the transpiration water consumption of A. georgei var. smithii in the Sejila Mountains of southeastern Tibet. Eight individuals of A. georgei var. smithii with different DBH were measured, as well as five meteorological factors. 【Result】 The diurnal variation of the sap flow displayed a single peaked curve on sunny days, and the average stem sap flow rates of the eight samples were 137.09, 142.71 and 184.43 g/h in July, August and September, respectively. The activity period of sap flow was from 10:00 to 22:00, and its peak value occurred at approximately 16:00. The transpiration water consumption per unit sapwood area was significantly positively correlated with air temperature and photosynthetic active radiation, and was positively correlated with saturated vapor pressure difference (VPD), but was negatively correlated with air relative humidity, and had no relation with wind speed. The ranking of correlation coefficients was air relative humidity > air temperature > photosynthetic active radiation > VPD. The DBH was significantly correlated with sapwood area (R 2=0.999) and transpirtation water consumption per day (R2=0.937). 【Conclusion】 The diurnal variation in the transpiration water consumption of A. georgei var. smithii was of “N” type, which was significantly affected by environmental factors, such as air temperature, humidity, and photosynthetic active radiation. The daily transpiration water consumption per plant increased rapidly with the increase in DBH.
Abies georgei var. smithii / transpiration water consumption / driving factor / southeastern Tibet
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<em>Aims</em> Water consumption of urban plants with multiple ecological effects is important. However, large errors may occur when sap flow is scaled from single point measurement to whole tree without knowledge of spatial sap flow profiles in the trunk. Our objective was to investigate the spatial variation of sap flux density (<em>J<sub>s</sub></em>) and its possible cause to estimate whole-tree water use more precisely.<em>Methods</em> Spatial patterns of sap flux density in the sapwood of <em>Pinus tabulaeformis</em>, <em>Cedrus deodara</em> and <em>Robinia pseudoacacia</em> were investigated with thermal dissipation probe from June to November 2008 in Beijing, China.<em>Important findings</em> Axial variation was substantial. Due to greater exposure to sun in the south aspect, the anatomy of the xylem structure and lower branch height, there was an apparent relationship between sap flux density and aspect in <em>P. tabulaeformis</em> and <em>C. deodara</em>, but no apparent relationship in <em>R. pseudoacacia</em>. Hourly <em>J<sub>s</sub></em> over 24 h at different aspects were highly correlated; therefore, mean <em>J<sub>s</sub></em> may be accurately estimated based on measurement obtained on one aspect. <em>J<sub>s</sub></em> showed marked radial variation within the trunk. <em>J<sub>s</sub></em> at different depths show similar diurnal pattern, while <em>J<sub>s</sub></em> at deeper depth lagged behind and was more sensitive to evaporative demand than the shallower depth. Hourly<em> J<sub>s</sub></em> over 24 h at different depths were highly correlated, so <em>J<sub>s</sub></em> at a particular depth could be extrapolated as a multiple of <em>J<sub>s</sub></em> at the depth of 15 mm. However, depth profiles of <em>J<sub>s</sub></em> differed among aspects within a tree. <em>J<sub>s</sub></em> at the deeper depth on the south aspect of <em>C. deodara</em> was greater and had no time lag compared to other aspects. In conclusion, sap flux density on the north side at depths of 15 and 70 mm could give an accurate estimation of whole-tree transpiration.
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