Leaf Transpiration Characteristics of Pear Tree

The transpiration rate,water use efficiency and its influencing factors of Pyrus bretschneideri Rehd.were studied using the CIRAS-1 infrared gas analyzer in Yangling of Shaanxi Province.The results indicated that transpiration rate showed mono-peak diurnal patterns,mostly peaked between 11:00 to 15:00.The seasonal change of transpiration rate showed ‘V’ pattern,which decreased from May to August,and then increased to the highest value in September.The average of seasonal transpiration rate was 2.66 mmol·m-2·s-1.The air temperature,leaf temperature and vapour pressure deficit were the major factors influencing diurnal changes in transpiration rate,which explained 85%～96%,76%～86% and 98% variations in transpiration rate,respectively.The diurnal peak of water use efficiency (WUE) occurred between 7:00 to 9:00,and then decreased slowly as the time moved.The seasonal variation of WUE showed that the WUE was the highest in August,which the value was 5.38 μmol CO2/mmol H2O;WUE were relatively similar in May,June,July and September,which the values between 2.86 to 3.05 μmol CO2/mmol H2O.The seasonal average of WUE was 3.44 μmol CO2/mmol H2O.Correlation analysis showed that WUE were influenced comprehensively by PAR,air temperature,leaf temperature,air humidity and vapour pressure deficit.