黄土高原半干旱区柠条(Caragana korsh inskii)树干液流动态及其影响因子

The sap flow dynamics of Caragana korshinskii and the influence of environmental factors in semi-arid region of the Loess Plateau

应用热脉冲技术在黄土高原神木县六道沟小流域于2006年6月13至25日测定了两种不同密度柠条(Caragana korshinskii)群落的树干液流动态。同时测量了土壤水分、太阳辐射、大气温度、相对湿度、风速、水汽压亏缺和作物参考蒸散等环境因子,并根据植物蒸腾的P-M公式,反推计算冠层导度。结果表明,除风速外,柠条树木液流与太阳辐射、大气温度、相对湿度、水汽压亏缺、作物参考蒸散均显著相关,且可用太阳辐射的线性表达式来估测。不同密度群落的日蒸腾量随叶面积指数增大而增加,叶面积指数为2.3的群落平均日蒸腾为3.83mm d-1m-2,而叶面积指数为1.1的林分平均日蒸腾1.64mm d-1m-2。冠层导度与气象因子关系复杂,当土壤水分不存在亏缺时,冠层导度与太阳辐射、大气温度、作物参考蒸散因子显著相关,与水汽亏缺和相对湿度因子无相关性;当土壤水分存在亏缺时,冠层导度与太阳辐射、大气温度、作物参考蒸散因子无相关关系,而与水汽亏缺和相对湿度因子显著相关。

Measurements of sap flow were made in two 20-year-old Caragana korshinskii stands that largely differed in tree density for the period of 13 -- 25 June 2006 in Liudaogou catchment in Loess Plateau of China. Soil water content, air temperature, relative humidity, solar radiation, wind speed, grass reference evapotranspiration （ET0） , and water vapor pressure deficit （VPD） were also measured, and the actual canopy conductance was calculated from the inverted Penman- Monteith equation based on the actual data of stand transpiration. The results showed that the sap flows were closely coupled to the changing weather conditions except wind speed and could be tightly fitted to a simple linear equation of radiation. The transpiration from the two studied stands was effectively scaled by leaf area index. Canopy transpiration of the high densilEy stand with LAI 2.3 reached in averaged of 3.83 mm d^-1 m^-2 compared with 1.64 mm d^-1 m^ -2 for the stand with LAI 1.1 of the low density stand. The analysis of canopy conductance showed no meaningful responses to radiation, air temperature and ET0 but excellent fits to VPD and relative humidity in the case of soil drought. On the contrary, no correlativity of canopy conductance to VPD and relative humidity was observed in case of soil wet condition, though canopy conductance was tightly fitted to radiation, air temperature and ET0.