在蒸腾旺盛的7,8月份,选择典型晴天,对5种不同密度(1400,1600,1800,2000,2200株/hm2)刺槐(Robinia Pseudoacacia L.)林的叶片含水量、蒸腾速率、叶水势、根水势日变化进行了观察,并测定了林地0—60cm土层的土壤含水量。结果表明,(1)各密度林分叶片含水量的日均值在7,8月份均为ρ2200>ρ2000>ρ1400>ρ1600>ρ1800,8月低于7月;(2)不同密度刺槐林蒸腾速率日变化趋势在7,8月份呈现相似的变化规律,即随着林分密度的增大,蒸腾速率日变化曲线由"双峰型"趋于"单峰型",最大值均出现在下午13:00—14:00,日平均蒸腾速率在7,8月份为:ρ1800>ρ1600>ρ1400>ρ2000>ρ2200;(3)不同密度刺槐林叶水势的日均值在7,8月份均为ρ1800<ρ1600<ρ1400<ρ2000<ρ2200,但8月份明显低于7月份,其日变幅则明显高于7月份;(4)根水势高于叶水势,日变幅小于叶水势日变幅,日均值大小在7,8月份均为:ρ1800>ρ1600>ρ1400>ρ2000>ρ2200,且8月份低于7月份,而日变幅则是8月份大于7月份;(5)不同密度刺槐林一天中根、叶水势之差(Δφ)与蒸腾速率(Tr)的关系可以用对数曲线来拟合;(6)刺槐的叶水势随着叶片含水量的增大而升高,二者的关系可以用对数曲线来拟合;(7)不同密度林地7月份土壤含水量随土层深度的增加变幅较小,而8月份变幅较大,0—60cm土层的土壤平均含水量随林地密度的增大而减小。从土壤水分的有效利用以及达到最佳生长状况的角度出发,建议试验区15年生刺槐林分密度为1800株/hm2。
Daily changes of leaf water content, transpiration rate, leaf water potential, and root water potential of Robinia Pseu doacacia from different stand densities and soil water within 60 cm of soil surface in the proving ground were studied on typical clear days during the peak season. Results are listed as following : (1) Daily average leaf water content of different stand densities was lower in August than J uly and was in the sequence ofρ2200>ρ2000>ρ1400>ρ1600>ρ1800 in the two months. (2) Diurnal variation of t ranspiration rate was similar in both months, meaning that the curves changed f rom“double peak”style to“single peak”with increased stand density and all the peak values appeared between 13 :00 and 14 :00. Daily average transpiration rate wasρ1800>ρ1600>ρ1400>ρ2000>ρ2200 in July and August . (3) Daily average leaf water potential of different stand densities was in the following order in both months :ρ1800<ρ1600<ρ1400<ρ2000<ρ2200 and was apparently lower in August than in July, with more obvious daily variation in August than in July. (4) Root water potential was higher than leaf water potential, with daily variation obviously less than leaf water potential, and daily average root water potential of five stands with different densities was in the order ofρ1800>ρ1600>ρ1400>ρ2000>ρ2200 and was lower in August than in July, with more obvious daily variation in August than in July.(5) Difference between leaf and root water potential ( S —L ) was negatively related with transpiration rate ( Tr) and such a relationship can befitted by logarihmic curve. (6) Leaf water potential of R. Pseudoacacia increases with leaf water content, the relationship between them can be described by logarithmic curve. (7) With the increased soil depth, soil water variation was lower in July than in August and the average soil water in 0 —60 cm layer declined with increased stand density. From the respective of effective water utilization and the best growth vigor, 1800 st rains/ hm2 is the reasonable stand density.