Preferential Allocation of Photosynthate toward Better Mutualists, Spatial Structure, and the Maintenance of the Arbuscular Mycorrhizal Mutualism

丛枝菌根（AM）真菌与大多数植物物种的根形成有益的联系，包括大多数作物植物。这些真菌增加了植物对固定土壤矿物质的获取，并反过来接收植物碳水化合物。虽然这种相互作用在植物和真菌之间是互利的，但真菌促进植物生长的程度因土壤环境和真菌分离而异。此外，观察到这种益处会随着时间的推移而增加和降低。目前，对这些动态的预测性理解几乎没有基础。最近的研究表明，植物可以优先将碳水化合物分配给最有益的真菌。这种优先分配允许有效真菌在面对非有益真菌的竞争时增加，前提是植物根系中真菌之间有足够的空间分隔。优先分配可以为理解有益真菌的持久性及其丰度随时间的变化奠定基础。本研究将测试优先分配的资源触发因素和环境依赖性，并测试植物和真菌物种之间的优先分配模式。最后，真菌种群对植物根系内真菌空间混合操纵的响应将被评估。这些结果将用于预测在不同环境梯度中有益真菌丰度的变化。拟议的研究将培训本科生，研究生和博士后科学家用于测量和操纵有益AM真菌的技术。此外，这项研究将为独立的本科生研究创造机会。特别是，一项测试菌根真菌如何有助于印第安纳大学校园原生草原恢复的实验将作为环境生物学非专业课程的一部分启动。因此，学生将接触到与此项目相关的生态学研究的多个方面。

Arbuscular mycorrhizal (AM) fungi form beneficial associations with the roots of most plant species, including most crop plants. These fungi increase plant access to immobile soil minerals and receive plant carbohydrates in return. While this interaction can be mutually beneficial between plants and fungi, the extent to which the fungi increase plant growth varies across soil environments and fungal isolates. Moreover the benefit has been observed to increase and degrade over time. Currently, there is little basis for predictive understanding of these dynamics. Recent work has demonstrated that plants can allocate their carbohydrates preferentially toward the most beneficial fungus. This preferential allocation allows the effective fungus to increase in the face of competition from non-beneficial fungi provided that there is sufficient spatial separation between the fungi within a plant's root system. Preferential allocation may form a foundation on which to understand the persistence of beneficial fungi and change in their abundance over time. The proposed work will test resource triggers and environmental dependence of preferential allocation and test patterns of preferential allocation across plant and fungal species. Finally, fungal population response to manipulation of spatial mixing of the fungi within the plant root system will be evaluated. These results will be used to develop predictions for changes in abundance of beneficial fungi across environmental gradients. The proposed research will train undergraduates, graduate students and postdoctoral scientists in techniques used to measure and manipulate beneficial AM fungi. In addition, this research will create opportunities for independent undergraduate research. In particular, an experiment testing how mycorrhizal fungi may benefit restoration of a native prairie on the campus of Indiana University will be initiated as part of a non-majors course in environmental biology. Students will thus be exposed to multiple aspects of ecological research related to this project.