Sap flow in tree trunks within Chaohe mountain area and its variation with meteorological factors

Abstract

【Objective】 Water ascent in plant is driven by water evaporation from leaves, influenced by meteorological factors. Understanding its variation with these factors is important to unveil the mechanisms underlying plant transpiration. This paper is to investigate the correlation between sap flow and meteorological factors in a plantation located in the Chaohe mountain area. 【Method】 The experimental site is at the Dadaigou Experimental Station in Fengning County. Sap flow from May to October in different tree species including Larix principis-rupprechtii, Pinus tabulaeformis and Hippophae rhamnoides, was measured using the Granier-type thermal dissipation probe. Meteorological data measured during the same period were used to analyze their impact on the sap flows. 【Result】 ① In sunny days, sap flow measured in all species increased in daytime and decreased in evening; it was larger in sunny days than in rainy days. Sap flow in Hippophae rhamnoides was faster and more sensitive to rainfall than other two species. ② Hourly sap flow in all species was positively correlated to atmospheric temperature (Ta), vapor pressure deficit (VPD), net radiation (Rn) and wind velocity (W), and negatively correlated to rainfall and relative humidity (Rh). Rn is the factor affecting sap flow most, followed by VPD, Ta and Rh. ③ Daily sap flow in Larix principis-rupprechtii, Pinus tabulaeformis and Hippophae rhamnoides was 2.78, 1.44 and 5.27 mL/(cm2·h) separately, affected significantly by Rn, VPD and Ta. ④ There was a significant delay in the response of sap flow to changes in meteorological factors for all three species, with the response to changes in VPD and Rn delayed by 20 min and 60 min for Larix principis-rupprechtii, 40 min and 50 min for Pinus tabulaeformis, and 20 min and 50 min for Hippophae rhamnoides, respectively. 【Conclusion】 The meteorological factors that affect sap flow in the three species in the Chaohe mountain area were net radiation (Rn) and vapor pressure deficit (VPD). There was a significant delay in the response of sap flow to changes in meteorological factors. Studying plant transpiration and its variation with meteorological factors should consider such a delay.

Keywords

• characteristics of sap flow
• meteorological factors
• scales
• time lag