岩溶区青冈栎整树蒸腾的季节变化

Seasonal variation of Cyclobalanopsis glauca whole-tree transpiration in karst region

应用Granier热消散树干液流技术,在裸露岩溶区坡地上对青冈栎样树的树干液流和整树蒸腾过程变化及其驱动因子进行了研究.结果表明:青冈栎树干液流密度与树木胸径大小的关系是随机的,日间液流密度峰值出现在13:30—14:30;日液流密度峰值夏季最大,为56.00g H2O·m-2·s-1,春季最小,在35.86g H2O·m-2·s-1.岩溶区单树日蒸腾量随着天气变化起伏较大,单树日蒸腾量与水汽压亏缺和太阳辐射呈显著的幂函数相关关系(R=0.97,P<0.01).平均整树日蒸腾量变化格型为夏季高冬春低,秋季(旱季)随土壤水分的减少由高到低变化.与其他地区的树种相比,即使受旱季的干燥少土双重胁迫,裸露岩溶区坡地上的青冈栎整树日蒸腾量仍然较高,推断在岩溶区旱季青冈栎的水分来源可能很大程度上依赖于富水的表层岩溶带.

By using Granier＇ s sap-flow method, the variations of sap flux density and whole-tree transpiration of Cyclobalanopsis glauca （ syn. Quercus glauca） on a hilly slope in the karst region of South China were studied, with their driving factors analyzed. The sap flux density （Js） of C. glauea varied randomly with the diameter of breast height of individual trees, and its maximum occurred at 13：30-14：30. In a seasonal course, the daily Js was the maximum （56. 00 g H2O · m^ -2 · s^-1 ） in summer, and the minimum （35.86 g H2O · m^-2 · s^-1 ） in spring. The daily wholetree transpiration had a greater change with weather condition, representing a power functional relationship with vapor pressure deficit （VPD） and photosynthesieally active radiation （PAR） （R = 0. 97 ,P 〈0. 01 ）. The average daily whole-tree transpiration tended to be high in summer and low in winter and spring, and decreased with the decrease of soil moisture content in autumn （ drought season）. However, comparing with that of the tree species in other regions, the daily whole-tree transpiration amount of C. glauca in study region was still higher, even though the weather was dry and the soil was thin. It was presumed that in the dry season in karst region, the water supply for C. glauea could be mainly depended on the water-rich epikarst.