古尔班通古特沙漠南缘梭梭茎干液流变化及其对环境因子的响应

利用TDP热扩散式茎流计，结合气象观测系统，对古尔班通古特沙漠南缘原生梭梭的树干液流及环境因子进行连续监测，分析了梭梭树干液流对环境要素的响应，基于潜在蒸散发和蒸腾需求指数对梭梭茎干液流进行了模拟。结果表明：（1）梭梭树干液流在晴天的日变化呈单峰曲线，液流速率上升阶段时间短于下降阶段时间，与气象因素的日变化规律不一致。不同季节梭梭树干液流速率日变化规律存在差异，夏季液流与春季、秋季相比，启动早，停止晚，峰值更大且发生更早。（2）环境要素间存在着不同程度的相关性，主成分分析表明：前三个主成分共能解释85%的环境信息，其中以空气湿度、空气温度、水汽压亏缺、潜在蒸散发、净辐射为主的第一主成分能解释47%环境信息变化，以土壤温度、水汽压为主的第二主成分能解释20%环境信息变化，以土壤含水量、风速为主的第三主成分能解释17.6%的环境信息变化。（3）在春季和夏季基于潜在蒸散发的S型模型模拟梭梭液流速率的精度更高，在秋季基于蒸腾需求指数模拟的梭梭液流速率的精度更高。（4）梭梭树干液流速率与大气水分亏缺、净辐射、潜在蒸散发之间存在非对称响应，且不同季节间的响应规律存在差异，在春季和秋季，液流速率与水汽压亏缺呈顺时针状，与净辐射、潜在蒸散发呈逆时针状；在夏季，液流速率与水汽压亏缺呈顺时针状，与净辐射、潜在蒸散发呈斜8字顺时针状。

Dynamics and responses of sap flow of Haloxylon ammodendron to environmental variables in the southern edge of the Gurbantünggüt Desert

The transpiration water consumption of Haloxylon ammodendron is an important physiological index, and its variation law is influenced by many environmental factors. The transpiration water consumption of individual trees could be accurately measured by investigating the characteristics of sap flow and environmental factors,and the transpiration of single-tree also could be predicted with the help of environmental indicators by building the model of the sap flow with environmental factors. Combined with automatic weather stations,a thermal dissipation probe(TDP)was continuously used to measure the sap-flow dynamics and environmental factors of Haloxylon ammodendron in the southern marginal zone of the Gurbantünggüt Desert,Xinjiang,China,the sap-flow velocity response to the environmental elements were analyzed and the stem sap flow of Haloxylon ammodendron were simulated based on the potential evapotranspiration and transpiration requirement index. Results show as follows:(1)The change of sap-flow velocity mainly presented single-peak curve,the time of the velocity rising stage was shorter than that of the descending stage,which was inconsistent with the diurnal variation of meteorological factors. There were differences with the amplitude of daily variation during different seasons,in summer,the sap-flow started earlier and stopped later,the peak value was higher and presented earlier compared with spring and autumn.(2)There were different degrees of correlation between environmental factors. The first three axes of principal component analysis(PCA)explained 47%,20%,17.6% of variances in the environmental data sets,while the first principal component including RH,T_a,VPD,ET₀ and R_n could explain 47% of environmental information changes;the second principal component with T_s and e_a could explain 20% of environment information;the third principal component given priority to H_S and u₂ could explain 17.6% of the environment change information. The first principal component reflects the needs of the atmosphere transpiration,and the second and third principal components reflect the effect of soil environmental conditions on transpiration rate. (3)The accuracy of sigmoid based on potential evapotranspiration in spring and summer was higher,and the polynomial model was better than the ET₀ model in autumn.(4)The hysteresis between velocity of sap flow and environmental factors was revealed in Haloxylon ammodendron,and presented significant differences in different seasons. In spring and autumn,the relationship between the velocity of sap flow and VPD was clockwise,while the relationship between the velocity of sap flow and the net radiation or the potential evapotranspiration presented a counterclockwise trend. During summer,however,the relationship between the sap flow velocity and the net radiation or potential evapotranspiration presented a clockwise of the figure 8. The water consumption of Haloxylon ammodendron and its response to environmental factors had significant differences in different seasons, which also provided the theoretical support for the study on the water consumption of desert plants and the management of artificial irrigated plants.