外来植物入侵对本地植物菌根真菌的影响及其机制的研究

We are confronted with the increasing risk of invasion by exotic plant species. The success of the exotic plants in invasive ranges can be achieved can be achieved not only by their high resource use efficiency but also by their potential to disrupt the mutualism in the native species. The mutualism between mycorrhizal fungi and plant roots is important for plant growth and development, and can be disturbed by exotic plants in promoting their invasion. However, we know little about the effects of exotic plant invasive on mycorrhizal associations of native plants, the underlying mechanisms, and how the effects vary with duration of the invasion. The knowledge gaps greatly hinder our understanding of the pathway of exotic plant invasion by disrupting mycorrhizal associations. In this project, we will compare mycorrhizal traits of one native plant in monoculture with those of the native plant in mixture with invasive plants. The mycorrhizal traits examined here include mycorrhizal fungi composition, diversity, functional proteins required in maintaining the mycorrhizal symbiosis, nutrient transports between roots and fungi and decaying the soil organic matter etc. We also examine traits of external hyphae as well as non-mycorrhizal fungi. We then explore relationships of the mycorrhizal and non-mcorrhizal traits with plant functional trait, soil nutrients and allelopathy of the exotic plants. By these analyses, we aim to reveal how invasive plants affect mycorrhizal association in native plants and how the effects vary with invasive duration. Results of this project will deepen our understanding about the relationship between the mutualism of native plants and the exotic plant invasion. We also can be enriched in the knowledge on the diversity of and interactions for the mechanisms through which exotic plants successfully dominate the invasive ranges. The results will also be instructive in laying down suitable approaches to control exotic plant invasions. Finally, this study is promising in shedding insights into our understanding of interspecies interactions between plants and between plants and microbes.

外来植物入侵成为人类面临的重大环境问题。外来入侵植物不但具有高效的资源利用效率，还可以通过干扰本地植物的共生关系实现入侵。菌根真菌和根系的共生是植物生长和发育的重要保障，对这种共生关系的破坏成为外来植物重要的入侵途径。然而，我们在外来植物对菌根真菌的影响、机制和时间效应方面的认识十分有限，这极大制约我们对这一入侵途径的认识。本项目通过对比本地植物单种和与入侵植物混种时，菌根真菌特征，包括组成、多样性、功能蛋白和根外菌丝，以及非菌根真菌的差异，分析这些差异与植物功能性状、土壤养分以及化感作用的关系，深入揭示入侵植物对本地植物菌根真菌的影响，这些影响随时间的变化，并阐明相关机制。项目的实施将大大推进我们对生物共生与外来植物入侵间关系的认识，深化对外来植物入侵机制多样性及其相互关系的理解，为防控入侵提供理论依据。项目结果也将对我们认识植物间相互作用以及植物与微生物间关系等方面有重要价值。

外来植物入侵对本地植物共生真菌的干扰是其入侵成功的重要因素。然而，相对于植物功能性状对外来入侵响应的研究，我们对根系共生微生物，如菌根真菌和根瘤菌的响应知之甚少。本项目通过一系列野外调查和盆栽实验，发现（1）与预期相反，生物量越大的入侵种(快策略)对本地植物苍耳菌根真菌的侵染率的影响越小(p = 0.003)，但对苍耳根的氮浓度的影响越大(p = 0.011)；入侵种对苍耳菌根真菌侵染率的影响与对苍耳根的氮浓度的影响为负相关(R2 = 0.37, p = 0.015)，苍耳根的氮浓度而非菌根真菌侵染率的变化量与植物的地上生物量为正相关(p = 0.017)。本地植物狗尾草的响应格局与苍耳的响应格局类似。入侵植物能够显著增加苍耳和狗尾草根中的真菌群落Alpha多样性指数(以Chao1指数为例)，但不影响苍耳、狗尾草和稗草的真菌群落结构。（2）对于具有双共生微生物体系（菌根真菌+根瘤菌）的本地豆科植物大豆来说，入侵植物瘤突苍耳显著降低大豆的根策略（细根生物量、根氮浓度），但对菌根策略没有影响，同时降低了根瘤数目，提高了根瘤的固氮活性；大豆的根策略与菌根策略无关，但根策略与根瘤策略呈显著负相关，即根系自身活性越强对根瘤的依赖性越小，表明大豆主要调整根策略和根瘤策略以响应瘤突苍耳的入侵。（3）遮荫时根瘤响应入侵植物的策略迥异：全光照时降低根瘤数目，提高活性，遮荫时降低根瘤数目，保持活性；随着遮荫程度进一步增加，大豆仅依赖根策略吸收养分。不同遮荫处理下，大豆根策略依赖的具体根性状不同，表明其根策略响应光环境变化的多样性。不同光强下，瘤突苍耳入侵均抑制大豆养分吸收的菌根策略(丛枝菌根真菌相对丰度)。（4）瘤突苍耳潜在化感物质咖啡酸影响大豆根瘤固氮活性和根瘤数目以及根策略，但不改变根瘤菌的组成；加入咖啡酸时大豆倾向于更加依靠根瘤固氮获取养分。这些研究结果充分表明，干扰根系共生微生物是外来植物成功入侵的一个重要机制，从而有助于入侵植物防控。