Strong Graham L, Bannister Peter
Botany Department, University of Otago, Dunedin, New Zealand.
Botany Department, University of Otago, Dunedin, New Zealand.Corresponding author; email:
Funct Plant Biol. 2002 Jan;29(1):89-96. doi: 10.1071/PP00159.
The daily field water relations and gas exchange of the temperate mistletoes Ileostylus micranthus (Hook.f.) Tiegh. and Tupeia antarctica Cham. et Schlecht. on various hosts were examined seasonally in Dunedin, New Zealand during 1996-1998. Mistletoes commonly have higher transpiration rates (E) than their hosts, and this is generally cited as the reason why mistletoes develop lower water potentials (ψ) than their hosts. The mistletoe-host pairs that we examined showed no significant overall differences in E and stomatal conductance (g), and we used them to test the hypothesis that lowered ψ in mistletoes result from higher E. Despite the lack of differences in E and g, osmotic potentials, predawn and daily minimum ψ (ψmin) were significantly more negative in mistletoes, although differences between host and mistletoe ψ were less on hosts with low osmotic potentials and ψ. Mistletoes maintained lower ψ than their hosts both when unshaded and under artificial shading, had lower ψ than hosts at equal E, but had shoot hydraulic resistances similar to that of their hosts. E and ψ of hosts and mistletoes tended to be coordinated only in summer, when hosts were most water-stressed. Mistletoes maintained higher relative water contents at turgor loss, symplastic water contents, and bulk moduli of elasticity (ε) than their hosts. We conclude that the lower ψ in these temperate mistletoes are a consequence of greater mistletoe E only when host ψ are low, but are otherwise maintained by greater succulence and higher ε than in their hosts.
1996 - 1998年期间，在新西兰达尼丁，对生长在各种寄主上的温带槲寄生小花寄生（Ileostylus micranthus (Hook.f.) Tiegh.）和南极寄生（Tupeia antarctica Cham. et Schlecht.）的日田间水分关系和气体交换进行了季节性研究。槲寄生的蒸腾速率（E）通常高于其寄主，这通常被认为是槲寄生的水势（ψ）低于其寄主的原因。我们研究的槲寄生 - 寄主对在E和气孔导度（g）方面没有显著的总体差异，我们用它们来检验槲寄生中ψ降低是由较高的E导致的这一假设。尽管在E和g方面没有差异，但槲寄生的渗透势、黎明前和每日最低ψ（ψmin）明显更负，尽管在具有低渗透势和ψ的寄主上，寄主和槲寄生的ψ差异较小。槲寄生在无遮荫和人工遮荫条件下都保持着比其寄主更低的ψ，在相同E时比寄主具有更低的ψ，但茎干水力阻力与寄主相似。寄主和槲寄生的E和ψ仅在夏季寄主水分胁迫最大时趋于协调。槲寄生在膨压丧失时保持较高的相对含水量、共质体含水量和弹性模量（ε）。我们得出结论，这些温带槲寄生中较低的ψ仅在寄主ψ较低时是由于槲寄生较高的E导致的，否则是由比寄主更大的肉质化程度和更高的ε维持的。
