Many studies have investigated the effect of parasitic plants on their hosts; however, few have examined how parasite impact is affected by host size. In a glasshouse experiment, we investigated the impact of the Australian native hemiparasitic vine, Cassytha pubescens, on a major invasive shrub, Ulex europaeus, of different sizes. Infected plants had significantly lower total, shoot, and root biomass, but the parasite’s impact was more severe on small than on large hosts. When infected, small but not large hosts had significantly lower nodule biomass. Irrespective of size, infection significantly decreased the host shoot/root ratio, pre-dawn and midday quantum yields, maximum electron transport rates, and carbon isotope composition, and the host nodule biomass per gram of root biomass significantly increased in response to infection. Infection did not affect host foliar nitrogen concentration or midday shoot water potential. Parasite biomass was significantly lower on small relative to large hosts, but was similar when expressed on a per gram of host total biomass basis. Parasite stem nitrogen, phosphorus, and potassium concentrations were significantly greater when C. pubescens was growing on small than on large hosts. Our results clearly show that C. pubescens strongly decreases performance of this major invasive shrub, especially when hosts are small. This suggests that C. pubescens could be used most effectively as a native biocontrol when deployed on smaller hosts.

中文翻译：

---

本地半寄生虫对主要入侵灌木的影响受到感染时宿主大小的影响。


许多研究调查了寄生植物对其寄主的影响；然而，很少有人研究寄主大小如何影响寄生虫的影响。在温室实验中，我们研究了澳大利亚本土半寄生藤本植物Cassytha pubescens对不同大小的主要入侵灌木Ulex europaeus的影响。受感染的植物的总生物量、芽和根生物量显着降低，但寄生虫对小型寄主的影响比对大型寄主的影响更严重。当感染时，小型而非大型宿主的根瘤生物量显着降低。无论大小如何，感染都会显着降低宿主芽/根比、黎明前和中午量子产率、最大电子传输速率和碳同位素组成，并且每克根生物量的宿主根瘤生物量因感染而显着增加。感染不影响宿主叶面氮浓度或午间枝条水势。相对于大型寄主，小型寄主生物量显着较低，但以每克寄主总生物量表示时相似。当C. pubescens在小型寄主上生长时，寄生虫茎的氮、磷和钾浓度显着高于在大型寄主上生长的情况。我们的结果清楚地表明，毛毛竹强烈降低了这种主要入侵灌木的性能，特别是当寄主较小时。这表明当部署在较小的宿主上时，毛毛念珠菌可以最有效地用作本地生物防治剂。