新疆杨树杆液流密度轴向差异的初步研究

利用热扩散技术(TDP)分别监测新疆杨冠基部、杆基部处液流密度的变化,并结合同步气象观测,分析液流密度与大气蒸发潜力(ET0)的关系,结果表明:典型晴天日,新疆杨树冠、杆基部的液流密度日变化格局总体上与大气蒸发潜力相一致,但前者与ET0的相关性更强,可用Hill函数式得到较好的拟合,而后者与ET0间呈斜率不等的线性关系;在午间,冠基部液流密度是杆基部的3倍以上,在清晨,冠基部液流比杆基部液流提前平均约1 h启动。冠、杆基部边材液流间的"净"量因季节而异,在生长旺盛的7、8月份略有"亏损",而在6、9月份略有"盈余",新疆杨单株日吸收水分量与冠层日失水量并不完全一致。6—9各月冠基部液流日平均通量一般呈晴天>云天>阴天的规律,这与太阳辐射及大气蒸发潜力的变化格局相一致,而基部液流有时会呈现出云天>晴天的趋势。

Difference of Sap Flow Rate of Populus bolleana Lauche along Trunk Axial Direction

The change of sap flow rate along axial direction of trunk is considered to be the important evidence that water storage is involved in internal sap flow circulation. Based on monitoring sap flow rate at both crown base and stem base of half-mature Populus bolleana Lauche during the main growth season with thermal dissipation probe technique (TDP), the relationship between sap flow rate (J_s) at two typical position and atmospheric evaporation potential (ET₀) obtained with synchronous meteorological elements was analyzed. It was found that the diurnal variation pattern of sap flow rate at both crown (J_s,u) and stem bases (J_s,d) were consistent with ET₀ in typical sunny days, but the former had more close correlation with ET₀, which fitted well with the Hill function formula, while that between the latter and ET₀ presented linear relation with different slopes. At noon, J_s,u could be three times of J_s,d, and started about 1 hour earlier than the latter in the early morning. The "net" sap flux between J_s,u and J_s,d changed with season, and was in a slight water-lose status in July and August but a slight water-surplus in June and September instead. Daily total amount of absorbed water was not completely consistent with water loss of crown. The average daily sap flux computed by J_s,u from June to September was in the sequence of sunny > cloudy > overcast, which was consistent with solar radiation and ET₀, while sap flux computed by J_s,d sometimes was cloudy > sunny, showing the traits of leveling water stress by accelerated water-absorption in cloudy days for mid-serious atmospheric stress.