沙柳不同方位枝条液流变化及主要影响因子

Nocturnal sap flow variation characteristics and main influencing factors of Salix psammophila branches in different orientations

研究不同方位夜间液流可以更好地了解夜间水分利用及方位差异。以3 a生沙柳为研究对象,采用热平衡包裹式液流仪(EMS 62)监测沙柳灌丛不同方位枝条液流速率,分析沙柳不同方位液流速率变化特征及其主要影响因子。结果表明:雨季前、雨季和雨季后沙柳液流速率强弱为北向>东向>南向>西向。雨季前沙柳灌丛各方位液流速率均呈“双峰”型曲线变化趋势,且北向液流速率到达第2峰值的时间延迟2 h左右,雨季与雨季后各方位液流速率均呈“几”字型曲线变化,且雨季期间液流启动与结束时间均延迟30 min左右。东、南、西、北各方位夜间液流占全天液流的比例均呈“U”字型曲线,且波动范围分别20%~46%、21%~41%、25%~43%和23%~43%。观测期内各方位夜间液流与相对湿度及饱和水汽压差均具有显著相关性(P<0.01)。雨季前与雨季期间各方位夜间液流与各气象因子均表现出较明显的线性关系(R^(2)>0.46),然而雨季后不同方位夜间液流与各气象因子的线性关系较弱(R^(2)<0.34)。这表明降雨直接影响各方位夜间液流的水分利用效率,且由于受到环境因子影响,沙柳的夜间液流速率在时空与方位上均存在显著差异。这可为研究夜间水分利用提供科学依据。

[Background]Salix psammophila is one of the tree species with the largest artificial afforestation area in desert areas of China.For a long time,the water use of S.psammophila in arid and rainy seasons has formed its own unique water consumption strategy,which is an important basis for studying the rationalization of water use.Therefore,it is of great significance to study the variation characteristics and main influencing factors of nocturnal sap flow of S.psammophila in different orientations for understanding the orientation difference of nocturnal water use of S.psammophila and its adaptability to the environment.[Methods]In this study,3-year-old S.psammophila was used as the research object,and the heat balance wrap stem flow meter(EMS62)and small weather station(HOBO U30)were used to simultaneously monitor the sap flow rate of S.psammophila in different directions and the changes of meteorological factors such as solar radiation(R),temperature(T_(a))and relative humidity(R_(H)).Combined with Pearson correlation analysis and multiple regression method.The characteristics and main influencing factors of the sap flow rate of S.psammophila in different directions were analyzed.[Results]1)The order of sap flow velocity of S.psammophila was north>east>south>west.2)Before the rainy season,the sap flow rate of S.psammophila in all directions showed a“bimodal”curve,and the time for the northward sap flow rate to reach the second peak was delayed by about 2 h.The sap flow rate in all directions the rainy season and after the rainy season showed a“several”curve,and the start and end time of sap flow the rainy season were delayed by about 30 min.3)The proportion of nocturnal flow in east,south,west,north to the whole day flow showed a U-shaped curve,and the fluctuation ranges were 20%-46%,21%-41%,25%-43%and 23%-43%.4)During the observation period,the correlation coefficient between nocturnal sap flow and relative humidity and saturated vapor pressure difference was P<0.01.Before the rainy season and the rainy season,the determination coefficient R^(2)between the nocturnal sap flow in each direction and the meteorological factors was greater than 0.46,but after the rainy season,the determination coefficient R^(2)between the nocturnal sap flow in different directions and the meteorological factors was less than 0.34.[Conclusions]Rainfall and other environmental factors directly affect the nocturnal sap flow rate of S.psammophila,and the degree of influence is different in different directions of S.psammophila.This study reveals the water use law of branches in different directions of S.psammophila,which can provide scientific basis for studying nocturnal water use.