桂林岩溶试验场不同地貌部位黄荆蒸腾作用的比较研究

Comparative Studies on Transpiration Characteristics of Vitex negundo at Different Geomorphological Positions at Guilin Karst Experimental Site

对桂林岩溶试验场5月份不同地貌部位(洼地、坡地和垭口)黄荆的蒸腾作用特征进行了比较研究。结果表明,黄荆的蒸腾速率日变化因不同地貌部位而有所不同。垭口表现为单峰型,在中午12∶30时左右出现峰值,没有出现明显的午休现象。洼地和坡地虽然都表现为双峰型,但坡地确实有午休现象,而洼地则与光照强度瞬间减弱有关。以日平均蒸腾速率进行比较,3个地貌部位从大到小的顺序为垭口>洼地>坡地。3个地貌部位黄荆蒸腾速率的差异与不同地貌部位的水热条件、土层厚度及接受光照的时间不同有关。对黄荆蒸腾速率与其影响因子的关系进行了逐步回归和最优子级回归分析,结果表明,影响黄荆蒸腾速率的主导因子是气孔导度、大气相对湿度和叶面温度,其中气孔导度的影响最大,且影响程度随地貌部位而有所不同。

Transpiration characteristics of Vitex negundo at different geomorphological positions （ depression, slope, saddle） at Guilin Karst Experimental Site were studied. The results showed that there were differences in daily variation of transpiration rate of V. ne growing in different geomorphological positions. The transpiration rate at saddle displayed one-peak pattern, which reached peak value at about 12： 30, and did not appear obvious noon depression phenomena. Although the transpiration rates at depression and slope displayed two-peak pattern, it was truly attributed to noon depression phenomena at slope, while at depression, it was related to the instantaneous decreasing of light intensity. The average daily transpiration rates were in sequence as saddle 〉 depression 〉 slope. The differences in transpiration among different geomorphological positions related to the differences in hydrothermal conditions, the thickness of soil layer, and the time length of accepting sunlight. Stepwise regression analysis and best subsets regression analysis between transpiration rate of V. negundo and its influence factors were made, and the results indicated that the dominant factors to affect transpiration rate of V. negundo were stomatal conductance, air relative humidity and leaf temperature. The influence of stomatal conductance was the greatest, and the influencing extent varied with the geomorphological positions.