毛乌素沙地新疆杨生长季节蒸腾耗水规律

利用热扩散(TDP)技术测算得到了时间步长为10min的毛乌素沙地21年生新疆杨蒸腾速率,并结合自动气象站同步测定的太阳辐射(Q)、空气温度(Ta)、相对湿度(HR)、风速(V)和降雨量(P)等气象要素,分析了杨树蒸腾速率时间变化特征以及气象因素对杨树蒸腾速率的影响,以期为毛乌素沙地杨树防护林的发展提供必要的生态耗水量的理论依据。结果表明,在生长季节(4—9月份),新疆杨蒸腾速率具有明显的时间变化特征。具体表现为:晴天状况下,各月份均表现为单峰曲线,除4月份外,其余月份峰值较宽。受太阳辐射等因素的影响,各月份峰值出现时间及最大蒸腾速率不尽相同;多云状况下,4、8、9月份新疆杨液流变化表现为单峰曲线,5—7月份表现为多峰曲线;阴天状况下,各月份新疆杨蒸腾变化均表现为单峰曲线,5—7月份液流启动早,蒸腾速率上升快,峰值宽,相比之下,4、8、9月份液流启动晚,蒸腾速率上升慢,峰值窄。在新疆杨主要生长季节,杨树单株总耗水量为5300.96L,各月耗水量差别不明显。耗水最大的月份为6月,单株总耗水量为1073.82L,占整个生长期总耗水量的20.26%,平均日耗水量为34.64L;4、5、7、8、9月份耗水量分别为819.79、944.89、911.11、782.92、768.43L,平均日耗水量分别为27.33、31.50、29.39、25.26、25.61L。蒸腾速率(Tr)与Q、Ta、HR、V等气象要素有很好的复相关性。说明影响新疆杨蒸腾的最主要气象因子为太阳辐射。

Variation Characteristics of Transpiring Water-consumption of Populus bolleana during Growing Season in Maowusu Sandy Area

The temporal variation of the transpiration of 21-year-old Populus bolleana Lauche, and its relationship with meteorological factors in Maowusu Sandy Area were studied. The aim of the study was to provide essential guideline for the development of shelter belt in Maowusu Sandy Area. The transpiration and meteorological factors were monitored continuously from April to September, 2004, with the help of Thermal Dissipation sap flow velocity Probe (TDP) and automatic weather station. The data were measured every 2 min and recorded as means over 10 min intervals by a data-logger (CR10X). Result showed that transpiration of P. bolleana had obvious change characteristics on temporal scale during the growing season (from April to September). The pattern of transpiration of P. bolleana showed single-peak curve under sunny days, and the transpiration in growing months displayed broad peak except in April. The peak time of transpiration varied due to the various weather conditions in different months. Under cloudy days, the transpiration showed double-peak curve in April, August and September and single-peak curve in May, June and July. Under overcast days, the transpiration showed singe-peak curve. From May to July, the sap flow started early, and then the transpiration increased rapidly, demonstrated with broad peak curve, while it was contrary to that of April, August and September. During the growing season, the total water consumption of a single tree was 5 300.96 L. No significant difference existed in water consumption among different months. The highest transpiration occurred in June, with the water consumption of 1 073.82 L, accounting for 20.26% of the total water consumption. Water consumption of P. bolleana in April, May, July, August and September were 819.79, 944.89, 911.11, 782.92 and 768.43 L, respectively. Transpiration per tree showed a good correlation with canopy solar radiation, air temperature, relative humidity and wind speed. The linear regression analysis shows that the solar radiation has close correlation with transpiration.