晋西黄土区辽东栎、山杨树干液流比较研究

Study on sap flow in forest of Quercus liaotungensis and Populus davidiana by using the TDP method

于2009年生长季(4—10月),应用TDP(Thermal Dissipation Probe)热扩散探针技术,并结合同步测定的太阳辐射、大气温度、空气饱和水汽压差及大气相对湿度等气象因子,分析了晋西黄土区15年生辽东栎、山杨树干液流的昼夜变化及季节变化规律,建立了液流速率与气象因子的关系模型。结果表明:辽东栎和山杨树干液流速率昼夜变化显著,4月份和7月份峰值出现的时间不一致。4月份两个树种的峰值出现在清晨或夜间,而7月份树种树干液流速率于中午前后达到高峰。4月份两个树种夜间的树干液流速率明显大于白天,山杨的树干液流于中午前后接近于零。4月份,辽东栎和山杨树干液流速率的峰值分别为2.808 cm/h和1.188 cm/h,最小值为0.218 cm/h和0 cm/h,日平均液流速率为1.440 cm/h和0.516 cm/h;7月份,辽东栎和山杨树干液流速率的峰值分别为12.276 cm/h和20.448 cm/h,最小值为0.144 cm/h和0.288 cm/h,日平均液流速率为3.656 cm/h和6.328 cm/h。7月份阴雨天时,辽东栎的液流速率峰值较晴天小,日平均液流速率是晴天的0.95倍,对山杨是0.75倍。4月份两树种树干液流速率的月平均值最低,只有1.106 cm/h和0.626 cm/h;6月份达最高值5.112 cm/h和8.214cm/h,分别是4月份的4.62倍和13.12倍。生长季(4—10月)的林分林木总蒸腾耗水量对于辽东栎林为201.14 mm,山杨林为56.43 mm,辽东栎林为山杨林的3.56倍。统计分析表明,影响树干液流速率的主要因子对辽东栎是大气温度和太阳辐射,对山杨是太阳辐射和空气饱和水汽压差。

Stem sap flow of 15-year-old Quercus liaotungensis and Populus davidiana trees on the Loess Plateau,western Shanxi Province,was measured with a thermal dissipation probe during the growing season from April to October,2009.Sap flow responses to meteorological factors,and diurnal and seasonal stem sap flow variations were analyzed.The objectives were to establish a sap flow rate model with meteorological factors and to provide a theoretical basis to establish a water-saving and drought-resistance model.Sap flow velocity（SFV） of both species exhibited diurnal patterns and was higher when soil water was abundant than during drought.The daily maximum SFV was in the morning or at night in April,while the stem sap flow increased sharply after sunrise and peaked around noon,and sap flow was weak or almost nonexistent from sunset to sunrise in July.The SFVs of both species at night were higher than during the day,which showed they suffered serious daytime water stress in April.The P.davidiana sap flow ＇noon-rest＇ might be caused by high temperature or high light intensity in April.The daily SFV maximum values in April in Q.liaotungensis and P.davidiana were 2.808 and 1.188 cm/h,respectively,the minimum velocities were 0.218 and 0 cm/h,and the average values were 1.440 and 0.516 cm/h.In July,the daily maximum values of SFV in Q.liaotungensis and P.davidiana were 12.276 and 20.448 cm/h occurring between 10：00 and 16：00,the minimum values were 0.144 and 0.288 cm/h,and the average sap velocities of the two species were 3.656 and 6.328 cm/h,which showed that there existed a significant difference between the two tree species.The daily maximum and minimum SFVs in April were higher in Q.liaotungensis,whereas in July the daily maximum（occurring between 10：00 and 16：00） and minimum SFVs were higher in P.davidiana.The daily maximum SFV on sunny days was higher than on cloudy days for Q.liaotungensis in July;the average SFVs on cloudy days was 0.95-fold that on sunny days and 0.75-fold that of P.davidiana.There was shorter duration peak on cloudy days than on sunny days to P.davidiana.The lowest average SFVs were recorded in April（1.106 and 0.626 cm/hfor Q.liaotungensis and P.davidiana respectively）,whereas the highest values were recorded in June（5.112 and 8.214 cm/h;4.62-and 13.12-fold those of April,respectively）.The estimated total water consumption used for tree transpiration for Q.liaotungensis was much higher than that of P.davidiana over the whole growing season（201.14 mm and 56.43 mm,respectively;the former was 3.56-fold that of the latter）.Diurnal changes in sap flow were closely related to changes in environmental variables,but the dominant environmental factors differed between the species.Air temperature and solar radiation were the main factors influencing diurnal changes in Q.liaotungensis SFV,whereas solar radiation and water vapor pressure deficit were the principal factors for P.davidiana.A statistical model to calculate SFV from micrometeorological data is provided.