民勤绿洲荒漠过渡带梭梭(Haloxylon ammodendron(C.A.Mey)Bunge)树干液流特征及其对环境因子的响应

利用Grainer热扩散式探针法(TDP)连续测定民勤绿洲荒漠过渡带生长季梭梭树干液流,并同步测定外界环境因子。研究了6—11月份不同直径梭梭树干液流日、季变化及其与外界环境因子的相关性。结果显示:(1)随月份的递增,不同直径梭梭树干液流通量(SV)晴天日变化波峰区逐渐缩减。并且在6—8月份,不同直径SV均表现出明显的"宽峰型"现象,且晴天SV明显高于阴、雨天;(2)随季节变化,不同直径梭梭SV波动性较大,直径越大其波动性越高;而梭梭SV未表现出随直径增大液流通量越大的现象;(3)6—11月梭梭树干耗水量先增后降,7月达最高峰,且直径越大,梭梭总耗水量越大;(4)梭梭树干液流与环境因子相关程度受不同天气、时间尺度的影响较大,晴天相关性略高于阴、雨天。空气温度、净辐射、饱和水汽压差是影响梭梭树干液流的主要气象因子。0—100cm土层以上0—250cm根幅区土壤水分对树干液流影响最显著。(5)同比古尔班通古特沙漠梭梭生长季(5—10月)总耗水量458—1044kg以及日均耗水量1.8—6.4kg/d,整个生长季(6—11月)民勤绿洲荒漠过渡带梭梭的总耗水量495—1232kg、日均耗水量为2.0—8.3 kg/d,两者耗水量近似。利用TDP技术测定梭梭耗水量具有一定的可靠性。

The effect of environmental factors on stem sap flow characteristics of Haloxylon ammodendron (C. A. Mey.) Bunge in Minqin oasis-desert

In arid and semi-arid ecosystems, water resources are the key ecological factor restricting the structure and function of the oasis-desert ecotone. The objective of the present study was to determine the effect of environmental factors on the characteristics of stem sap flow and water consumption of Haloxylon ammodendron in the whole growing season. Thermal dissipation sap flow velocity probes (TDPs) and an automatic weather station were used to measure sap flow velocity in trunks of different diameters, and environmental factors such as air temperature (T), relative humidity (RH), solar net radiation (Rn), vapor pressure deficit (VPD), and precipitation (P), respectively, in the Minqin oasis-desert ecotone, Gansu Province, China, from June to November 2014. On clear days, the peak wave area of daily sap flow velocity (SV) of H. ammodendron trunks of different diameters gradually reduced with changing seasons, whereas the phenomenon "broad peak shape" of SV showed as excessive growth from June to August. The SV on cloudy or rainy days was lower than that on sunny days. The SV of different H. ammodendron trunk diameters often fluctuated, furthermore the larger the diameter, the higher the fluctuating during the growing season. However, there was no obvious consistency and relationship between SV and stem diameter. From June to November, the water consumption of H. ammodendron initially decreased, and the highest peak SV was in July. The larger the stem diameter, the water consumption was more higher. Environmental factors correlated positively with SV in different time scales and weather conditions. The weather condition effected the SV correlation of H. ammodendron significantly, where it was higher on sunny than on cloudy and rainy days. The correlation of SV with VPD was the highest with the total weather factors on sunny and rainy days, while the correlation of SV with Rn was the highest on cloudy days. In the study period, the correlation coefficitents between SV and T exceeded 0.842 (P<0.01). Rn was the second-most important influence on SV (R²=0.811, P<0.01), with the third influence factor of VPD (R²=0.769, P<0.01). The correlation of SV with soil moisture in the root area at 0-250 cm level points and 0-100 cm depths was the most significant. Therefore, from the results it could be deduced that H. ammodendron of Minqin is an efficient drought-resistant plant.