How do interactions between herbivores and mycorrhizal fungi regulate production of plant signalling compounds and parasitoid behaviour?

当植物受到食叶动物的攻击时，最令人着迷的适应性反应之一是向大气中释放化学信息素。这些挥发性的信号化合物可以传播很远的距离，并被寄生蜂检测到，寄生蜂用它们来定位和寄生食叶动物。在许多情况下，研究表明某些拟寄生虫仅对特定的信息化学物质产生反应，并且它们是由植物系统产生的。这种信息素释放机制有可能成为植物控制蚜虫种群的有效策略。植物枝条、蚜虫和寄生性天敌之间的三向相互作用已得到较好的了解。然而，很少有研究的一个有趣的额外的层面的故事-地下途径的化学信息素转移和叶食草动物之间的关系，植物根系和有益微生物在根际。高度简化的水培系统有证据表明，植物有可能将化学信息素释放到根际，供邻近植物吸收。在自然土壤中，存在通过菌根真菌在植物之间直接传递信息化学物质的可能性。这些真菌大量定植在几乎所有陆地植物的根部，并产生大量的菌丝体，将单个植物连接成一个共同的网络。有人认为，它们可能能够作为管道，将化学信息素转移到散装土壤和未受蚜虫感染的邻近植物中，这一假设尚未得到验证。虽然迄今为止进行的许多实验已经确定了特定生态成分的重要性，但显然需要采取更全面的方法来确定植物信号传导的自上而下和自下而上控制以及化学信息素转移的间接和直接途径的相对重要性（布鲁斯和皮克特，2007年）。因此，这个博士生项目将首先寻求确定叶食草动物对关键功能性状（营养通量）和菌根真菌多样性的影响，其次确定化学信息素在植物之间转移的地下途径。这些目标将通过检验以下假设来实现：1.蚜虫对植物的侵染影响了菌根真菌功能多样性; 2.蚜虫侵染改变了植物向根际和菌根际的化学信息素释放; 3.根际和菌际化学信息物质的间接传递发生在不同植物种之间; 4.常见的菌根菌丝体网络能够直接将化学信息素从植物转移到植物; 5.丛枝菌根真菌和蚜虫之间相互作用的结果取决于每种生物的定殖程度和真菌的种类组成。这项工作将使用基于微宇宙的系统的组合，增加生物的复杂性。这种方法意味着我们可以识别关键机制，同时控制潜在的混淆因素，管理项目风险，并建立更具生态相关性的系统。本工作首先以蚕豆（Vicia faba L.）作为测试物种。这种植物容易形成丛枝菌根，并产生化学信息素时，蚜虫侵扰。将开发盆栽实验，使植物成为共同的菌丝体网络整合，并选择个人将与蚜虫和寄生虫的反应，这种治疗措施。这些测量将在CASE合作伙伴的实验室使用嗅觉计和摄像机技术进行。采用13 CO2和33 P脉冲追踪实验、分子群落分析（TRFLP）等方法研究蚜虫对菌根真菌的影响。

One of the most fascinating adaptive responses by plants when they are subjected to attack by leaf herbivores is the release of semiochemicals into the atmosphere. These volatile signalling compounds can travel significant distances and are detected by parasitoid wasps that use them to locate and parasitise leaf herbivores. In many cases, it has been shown that certain parasitoids respond only to particular semiochemicals and that they are produced systemically by the plant. This mechanism of semiochemicals release has potential to be an effective strategy by plants for control of aphid populations. The three-way interaction among plant shoots, aphids and parasitoids is relatively well understood. However, there has been very little research on an intriguing additional dimension to the story - that of below ground pathways of semiochemicals transfer and the relationship between leaf herbivores, plant roots and beneficial microorganisms in the rhizosphere. There is evidence from highly simplified hydroponic systems that plants have the potential to release semiochemicals into the rhizosphere, which are available for uptake by neighbours. In natural soils, there is the possibility of a direct transfer process of semiochemicals between plants via mycorrhizal fungi. These fungi heavily colonise the roots of virtually all land plants and produce vast lengths of mycelium that interlink individual plants into a common network. It has been suggested that they may be able to act as conduits for transfer of semiochemicals into bulk soil and to neighbouring plants uninfected by aphids, a hypothesis that remains untested. While many of the experiments undertaken to date have identified the importance of particular ecological components, it is clear that a more holistic approach needs to be undertaken to determine the relative importance of top-down and bottom-up controls of plant signalling, and indirect and direct pathways of semiochemical transfers (Bruce & Pickett, 2007). This PhD studentship therefore will, firstly, seek to determine the impact of leaf herbivores on the key functional traits (nutrient fluxes) and diversity of mycorrhizal fungi, and secondly, identify the below ground pathways by which semiochemicals are transferred between plants. These aims will be achieved by testing the following hypotheses: 1. Aphid infestation of plants affects the functional diversity of mycorrhizal fungi; 2. Aphid infestation of plants modifies semiochemical release into the rhizosphere and mycorrhizosphere; 3. Indirect transfer of semiochemicals in the rhizosphere and mycorrhizosphere occurs between different plant species; 4. Common mycorrhizal mycelial networks enable direct plant-to-plant transfer of semiochemicals; 5. The outcome of interactions between arbuscular mycorrhizal fungi and aphids is dependent on the degree of colonisation of each organism, and the species composition of the fungi. The work will use a combination of microcosm based systems of increasing biological complexity. This approach means that we can identify key mechanisms while controlling potentially confounding factors, manage project risk and build up to more ecologically relevant systems. The work will in the first instance use broad bean (Vicia faba L.) as a test species. This plant readily forms arbuscular mycorrhizas and produces semiochemicals when infested with aphids. Pot experiments will be developed to enable the plants to become integrated into common mycelial networks, and selected individuals will be infested with aphids and the response of parasitoids to this treatment measured. These measurements will be made at the CASE partner's laboratory using olfactometer and video camera techniques. The impacts of aphids on mycorrhizal fungi will be determined using 13CO2 and 33P pulse chase experiments, molecular community profile analysis (TRFLP).