Transpiration Characteristics of Chinese Pines (Pinus tabulaeformis) in an Urban Environment

Abstract

Urban environments can significantly influence the transpiration of isolated plants. Therefore, optimal green space design, tree species selection, and tree maintenance require that the water use patterns of urban plants be quantified. In this study, the transpiration from individual Chinese pines (Pinus tabulaeformis) in the center of Beijing, China was measured continuously over a 2-year period. The response of whole-tree transpiration (E t) to environmental factors was investigated in multiple time scales. Maximum sap flux density (J s) ranged from 3.34E-05 to 8.2E-03 cm/s. E t was much higher in summer (32.93 kg/day) than in winter (6.22 kg/day). E t in the urban environment was much higher than that reported for Chinese pines with similar diameters at breast height (DBH) during 2000–2005 in suburban Beijing. Great differences were observed in the response of E t to environmental factors at different time scales. At the diurnal scale, hourly mean J s was linearly related to photosynthetically active radiation (PAR) and vapor pressure deficit (D), whereas at the daily scale, daily mean E t was linearly related to PAR, air temperature (T a), and soil water content (SWC), and was curvilinearly related to D. At the annual scale, E t was similar in the growing seasons of 2008 (a wet year) and 2009 (a dry year), even though the annual precipitation (P) and irrigation times were significantly different (724.8 vs. 432.8 mm; 2 vs. 12). From this result, it can be concluded that urban soil water conditions affected by both P and irrigation practice were a major cause of interannual E t variation.