Pate John S, Davidson Neil J, Kuo John, Milburn John A
Department of Botany, The University of Western Australia, 6009, Western Australia, Australia.
Department of Botany, The University of New England, 2350, Armidale, New South Wales, Australia.
Oecologia. 1990 Sep;84(2):186-193. doi: 10.1007/BF00318270.
Water relations of the root hemiparasite Olax phyllanthi were compared with those of its major species of hosts in natural habitat in coastal heath near Denmark, SW Australia. Leaf water potentials of Olax during winter were 0.4 to 1.4 MPa lower (more negative) than those of all (29) non parasitic host species examined. During the dry summer months (January to March), shallow-rooted hosts developed water potentials up to 3 MPa lower than those of Olax, and were accordingly rated as no longer accessible as a source of water to the hemiparasite. By contrast, deep-rooted hosts, with access to the water table, showed water potentials less negative than Olax, and haustorial contacts retained with these apparently enabled continued extraction of water and nutrients throughout the summer. Three other species of root hemiparasites parasitized by Olax, but not themselves parasitizing Olax, showed leaf water potentials throughout the year very close to, and mostly slightly more negative than those of Olax. Nocturnal measurements of leaf water potential in winter (July and August) in soil at field capacity (water potential -0.006 MPa) showed maintenance of a 0.5-0.8 MPa potential difference between Olax and a range of common host species. By dawn most hosts had equilibrated with the water potential of the soil, whereas both exposed and bagged Olax plants recorded potentials of -0.8 MPa. Daytime rates of transpiration and photosynthesis of Olax were less than those of a range of common hosts, but water use efficiencies were not consistently different between hemiparasite and hosts. This was reflected in almost identical mean values for carbon isotope ratio (C/C) between Olax (mean δ value -27.0) and thirteen frequently exploited hosts (δ value -27.1). The results are discussed in relation to published information on other angiosperm hemiparasites.
在澳大利亚西南部丹麦附近沿海石南荒原的自然栖息地中，对根半寄生植物 Phyllanthi 欧勒寄生草与其主要寄主物种的水分关系进行了比较。冬季，欧勒寄生草的叶片水势比所有（29种）被检测的非寄生寄主物种低0.4至1.4兆帕（更负）。在干燥的夏季月份（1月至3月），浅根寄主的水势比欧勒寄生草低达3兆帕，因此被认为不再是半寄生植物可利用的水源。相比之下，能接触到地下水位的深根寄主，其水势比欧勒寄生草的负性小，与这些寄主保持的吸器接触显然使半寄生植物在整个夏季都能持续获取水分和养分。另外三种被欧勒寄生草寄生但自身不寄生欧勒寄生草的根半寄生植物，全年的叶片水势与欧勒寄生草非常接近，且大多略比欧勒寄生草更负。在田间持水量（水势为-0.006兆帕）的土壤中，冬季（7月和8月）对叶片水势进行夜间测量发现，欧勒寄生草与一系列常见寄主物种之间维持着0.5至0.8兆帕的势差。到黎明时，大多数寄主已与土壤水势达到平衡，而暴露和套袋的欧勒寄生草植株记录的水势均为-0.8兆帕。欧勒寄生草的白天蒸腾速率和光合速率低于一系列常见寄主，但半寄生植物和寄主之间的水分利用效率并非始终不同。这反映在欧勒寄生草（平均δ值为-27.0）与13种经常被利用的寄主（δ值为-27.1）之间几乎相同的碳同位素比率（C/C）平均值上。文中结合已发表的关于其他被子植物半寄生植物的信息对结果进行了讨论。
