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通过测定成熟马占相思叶片的水势、气孔导度、蒸腾速率(Tr)、叶面积指数、边材面积等参数,研究了湿季(5月)和干季(11月)叶片的水力导度(Kl)、水分和光合特性的关系.结果表明:高大植株(平均树高20m、胸径0.26m)的边材面积与叶面积的比率(Asp/Acl)比较小植株(平均树高14.5m、胸径0.19m)高8.5%,前者的木质部水分通量大于后者,以支持冠层叶片的水分利用.对木质部易损曲线进行分析,Kl降低50%时,湿、干季的叶片水势(Ψl)分别为-1.41和-1.55MPa,且干季的木质部空穴化的易损性高于湿季.湿、干季的Kl峰值分别为5.5和4.5mmol·m-2·s-1·MPa-1,最大蒸腾速率(Trmax)分别为3.6和1.8mmol·m-2·s-1,且湿季的Kl和Trmax明显大于干季.一天中Kl和Tr的多次波动反映了木质部空穴化和修复的往复循环,叶片气孔在Kl降低超过50%或Ψl达到-1.6MPa时关闭,气孔导度在K1达到50%前仍保持较高水平.干季的水力导度与光合速率的相关性较湿季明显.季节更迭导致叶片水力导度损失是Tr和CO2交换下降的原因.
The hydraulic conductivities of leaves in wet season (May) and dry season (November) were studied by measuring the water potential, stomatal conductance, transpiration rate (Tr), leaf area index and sapwood area of mature Acacia mangium leaves (Kl), water content and photosynthetic characteristics of the plants were studied.The results showed that the ratio of the area of sapwood to leaf area (Asp / Acl) of tall plants (average tree height 20m, DBH 0.26m) Diameter of 0.19 m) was 8.5% higher than that of the former in order to support the water use of the canopy leaf.The fragile curve of the xylem was analyzed.When the Kl decreased by 50%, the leaf water potential (Ψl ) Were -1.41 and -1.55 MPa, respectively, and the vulnerability of xylem cavitation in dry season was higher than that in wet season.The Kl peak values of wet and dry seasons were 5.5 and 4.5 mmol · m -2 · s-1 · MPa -1, and the maximum transpiration rate (Trmax) was 3.6 and 1.8 mmol · m-2 · s-1, respectively, and Kl and Trmax in wet season were significantly greater than those in dry season.Multiple fluctuations in Kl and Tr in one day reflected the xylem holes The stomatal conductance of the leaves closed at a reduction of Kl> 50% or Ψl of -1.6 MPa, and stomatal conductance remained high until K1 reached 50%. The hydraulic conductivity of the dry season Relevance than the wet season photosynthetic rate significantly. The seasons result in the loss of leaf hydraulic conductivity is the reason Tr and CO2 exchange decline.