古尔班通古特沙漠南缘梭梭(Haloxylon ammodendron)群落能量平衡及蒸散特征

梭梭是北方荒漠区重要的固沙植物,具有较强的荒漠环境适应能力。研究梭梭群落能量及蒸散变化对科学管理水资源、保护与建设生态植被等有重大意义。基于波文比自动观测系统在古尔班通古特沙漠南缘丘间地实时连续测定的2018年气象和能量数据,运用波文比-能量平衡法对梭梭群落能量平衡和蒸散特征进行了分析。结果表明:梭梭生长季(4—10月)太阳净辐射和土壤热通量的日变化呈单峰状分布,净辐射通量最高值出现在13:30左右,土壤热通量最大值出现时间比净辐射推迟2 h,波文比在梭梭生长旺盛期全天变化稳定,萌发期和枯落期白天变化较小,夜间波动较大,湍流通量以显热通量为主;在晴天和阴雨天条件下,梭梭生长旺盛期的日蒸散量均明显大于萌发期和枯落期,且日蒸散量在旺盛期呈双峰型,萌发期和枯落期呈单峰型;2018年梭梭生长季蒸散量为279.67 mm,日均蒸散强度1.31 mm/d,梭梭群落的蒸散受到气象、自身生长特性以及土壤水分的影响,4月蒸散强度开始逐渐增大,由于多阴雨天气导致6月的蒸散强度有所降低,7月达到最大,9—10月水分、温度等条件缺乏,梭梭生理活动微弱,蒸散强度急剧减小。

Energy balance and evapotranspiration characteristics of Haloxylon ammodendron community in the southern margin of the Gurbantunggut Desert

Haloxylon ammodendron is an important sand-fixing plant in the desert area of north China,which has a very strong ability to survive in high temperature, drought, severe cold and barren desert environment. Evapotranspiration, as the main component of water balance and energy balance in arid desert ecosystem, is an important link between its ecological process and hydrological process. It is of great significance to study the energy balance and evapotranspiration of Haloxylon ammodendron community for scientific management of water resources, protection and construction of ecological vegetation, improvement of ecological environment and maintenance of oasis stability. Based on the meteorological and energy data measured by the Bowen ratio system on the southern edge of the Gurbantunggut Desert in 2018, the energy balance and evapotranspiration characteristics of the Haloxylon ammodendron community were analyzed by Bowen ratio-energy balance method. The results showed that during the growth period of Haloxylon ammodendron, the daily changes of solar net radiation and soil heat flux were distributed in a single peak. The highest value of net radiant flux appears at around 13:30 noon. The appearance time of the maximum value of soil heat flux had a hysteresis, which was delayed by 2 h than the net radiation. Bowen ratio changed steadily throughout the day in the strong growth period. For the germination period and the withering period, Bowen ratio was relatively stable in daytime, unstable during nighttime. Haloxylon ammodendron grew in an arid and waterless environment for a long time, and the evapotranspiration became smaller. Therefore, sensible heat energy transfer was main component in growth season. Under sunny and rainy days, the daily evapotranspiration in the strong growth period was significantly greater than that in the germination period and the withering period. The daily evapotranspiration showed a double-peak type in the strong growth period, a single-peak type in the germination period and the withering period. The evapotranspiration in the growing season of Haloxylon ammodendron was 279.67 mm, and the average daily evapotranspiration intensity was 1.31 mm/d. The evapotranspiration of Haloxylon ammodendron community was affected by weather, self-growth characteristics and soil moisture. The evapotranspiration intensity began to increase gradually in April and decreased in June due to rainy weather. The evapotranspiration reached its maximum in July. Because of the lack of moisture and temperature in September-October, the physiological state of Haloxylon ammodendron started to wither and fall, and the intensity of evapotranspiration decreased sharply.