基于热扩散技术的梭梭树干液流特征研究

Characterization of stem sapflow Haloxylon ammodendron by using thermal dissipation technology

利用TDP热扩散式茎流计,结合自动气象站,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,建立了生长季梭梭树干液流与环境因子的关系,估算出梭梭群落的日、季耗水量。结果表明:(1)液流速率日变化主要为单峰曲线,夏季偶有出现双峰曲线,不同季节间的液流速率大小差异显著,夏季树干液流启动早,峰值出现早,夜间持续有微弱的液流;(2)梭梭树干瞬时液流速率与风速、净辐射、空气温度、饱和水汽压亏缺值等因素呈显著正相关,与实际水汽压和空气湿度呈极显著负相关,影响梭梭树干瞬时液流速率变化的关键因子是净辐射和饱和水汽压亏缺值是导致树干液流速率瞬时变化的关键因子;(3)梭梭树干日均液流速率与净辐射、空气温度、实际水汽压、土壤含水率和土壤温度等呈极显著正相关,与空气湿度等呈极显著负相关,与风速相关性不显著,影响梭梭日均液流速率变化的关键因子是净辐射、饱和水汽压亏缺和空气温度。

The transpiration water consumption of Haloxylon ammodendron is an important physiological index, which is greatly influenced by many environmental factors. We accurately measured the transpiration water consumption of the individual trees by investigating their sap-flow characteristics in response to various environmental factors. We predicted the transpiration of a single tree with the help of the environmental indicators by building a sap-flow model and environmental factors. Combined with the automatic weather stations, a thermal dissipation probe （TDP） was used to continuously measure the sap-flow dynamics and environmental factors of H. ammodendron in the southern marginal zone of the Gurbantunggut Desert, China. The response of sap-flow velocity to the environmental factors was analyzed, and a relationship was established between the stem sap flow and environmental factors during the growing season of H. ammodendron. The results showed that： （1） the change of sap-flow velocity mainly presented a single-peak curve, or occasionally, a double-peak curve in summer. The amplitudes of daily variation and sap-flow peak were relatively greater in summer than in spring and autumn, and presented a significant difference with the sap-flow velocity during different seasons. In summer, the initial and peak sap-flows were observed earlier in the day, but a weak sap-flow was observed at night. （2） In the growingseason, the net radiation, air temperature, and saturated vapor pressure deficit were the key factors leading to the instantaneous changes in sap flow. The instantaneous sap-flow of H. ammodendron was positively correlated with wind speed, net radiation, saturated vapor pressure deficit, and air temperature, and negatively correlated with actual water vapor pressure and air humidity. （3） The key factors affecting the seasonal change in sap-flow velocity included net radiation, saturated vapor pressure deficit, and air temperature. The daily average flow rate was positively correlated with net radiation, air temperature, saturated vapor pressure deficit, actual water vapor pressure, soil water content, and soil temperature, and negatively correlated with air humidity. （4） The daily transpiration first showed an increasing trend, and then decreased during the whole growing season. In early May, the daily transpiration was 0.21 mm/d, and in the middle of June, it showed a peak-value, which lasted for forty days. The daily transpiration began to decline in late July until it reached a value of 0.10 mm/d. In H.ammodendron study samples, the daily transpiration was 0.35 mm/d and the total transpiration during the entire study period was 53.35 mm, suggesting strong ecological adaptability of H. ammodendron to drought conditions. In the study area, where the ecological environment was harsh because of high temperature and little rain, the water consumption of H. ammodendron was very low, making it the first choice to be used as the ecological restoration and reconstruction shrub in an arid land.