Davidson Neil J, True Kathryn C, Pate John S
Department of Botany, The University of Western Australia, 6009, Nedlands, Western Australia.
Oecologia. 1989 Aug;80(3):321-330. doi: 10.1007/BF00379033.
Seasonal and diurnal gas exchange and water relations of Amyema linophyllum and its host Casuarina obesa were studied at Gingin Western Australia. As recorded elsewhere for other species of mistletoe, stomatal conductances and transpiration rates were consistently higher in parasite than host, but assimilation rates did not differ significantly between partners, and water use efficiency was accordingly substantially lower in the parasite. Parallel responses of the species to environmental conditions suggested closely coordinated stomatal behaviour. However, sunlit and artifically shaded clumps of Amyema maintained high leaf conductances even when foliage fell below turgor loss point, yet their tissue capacitance values indicated maintenance of greater tissue water reserves during stress than in the host. Pressure-volume relationships indicated that differences in tissue water relations were unlikely to contribute significantly to the observed gradient in leaf water potential between partners. An experiment measuring changes in water potential of freshly detached host: parasite systems cut with the host shoot end immersed in water indicated that the haustorial junction was the principal site of resistance to transpiration-driven water flow into the parasite. A parallel experiment on intact attached shoots with mistletoe clumps enclosed and darkened just before dawn, demonstrated that, once the host commenced rapid transpiration, the water potential gradient between partners became reversed.
在西澳大利亚的金金地区，对柳叶钝果寄生及其寄主木麻黄的季节性和昼夜气体交换以及水分关系进行了研究。正如其他地方对其他槲寄生物种的记录一样，寄生植物的气孔导度和蒸腾速率始终高于寄主，但二者的同化速率没有显著差异，因此寄生植物的水分利用效率显著较低。这两个物种对环境条件的平行响应表明气孔行为密切协调。然而，即使叶片低于膨压丧失点，柳叶钝果寄生受阳光照射和人工遮荫的植株仍保持较高的叶片导度，但其组织电容值表明，在胁迫期间，它们比寄主维持更多的组织水分储备。压力-容积关系表明，组织水分关系的差异不太可能对观察到的寄主与寄生植物之间叶片水势梯度产生显著影响。一项实验测量了新鲜分离的寄主-寄生植物系统（寄主茎端浸入水中）水势的变化，结果表明，吸器连接处是蒸腾驱动的水分流入寄生植物的主要阻力部位。另一项对完整附着枝条进行的平行实验，在黎明前将槲寄生植株封闭并遮光，结果表明，一旦寄主开始快速蒸腾，寄主与寄生植物之间的水势梯度就会逆转。
