Cooperation and punishment in the arbuscular mycorrhizal symbiosis

丛枝菌根（AM）共生关系可以说是世界上最丰富和最重要的互惠共生关系，它将大多数陆地植物物种的根和AM真菌聚集在一起，具有巨大的互利优势。真菌的根外菌丝体作为根系的延伸，并增加对营养物质的吸收，如磷酸盐和氮，以及微量元素，如铜和锌。作为对养分吸收有益影响的交换，寄主植物将其吸收的碳的4%至20%转移给AM真菌。然而，AM共生没有遵循其他众所周知的互惠关系中稳定合作的约束条件，尽管它很重要，但控制合作伙伴之间合作行为的机制在很大程度上是未知的。本项目的目标是回答以下问题：(i)真菌菌株和植物宿主能否检测到不合作的伙伴；（ii）合作伙伴控制互动和惩罚不合作的生理机制是什么；（三）合作伙伴的多样性如何影响惩罚的力度？这些问题将通过(i)示踪实验来研究，以确定合作伙伴和非合作伙伴的成本效益比，并跟踪不同条件下合作伙伴之间的资源分配；（ii）独特的3室根器官培养来操纵伙伴的背叛和合作水平；（iii）稳定同位素探测来跟踪模拟生态系统中不同伙伴的碳分配。(4)微观实验，确定植物多样性如何影响不同真菌菌株的惩罚和适合度。通过对细胞、整株、植物群落三个层面相互作用的研究，确定了AM共生中稳定合作行为的不同尺度。AM共生负责全球生态系统中大量的养分转移，对全球生态系统的稳定性和生产力起着关键作用。研究这些过程对于最大化共生的生态系统和农业效益至关重要。该项目将为本科生和研究生提供培训，这些学生将成为国际合作项目的成员，并将有机会在荷兰和加拿大的合作者的实验室工作。

The arbuscular mycorrhizal (AM) symbiosis is arguably the world´s most abundant and important mutualism, and brings together the roots of the majority of land plant species and AM fungi to great mutual advantage. The extraradical mycelium of the fungus acts as an extension of the root system and increases the uptake of nutrients, such as phosphate and nitrogen, but also of trace elements such as copper and zinc. In exchange for the beneficial effects on nutrient uptake, the host plant transfers 4 to 20% of its assimilated carbon to the AM fungus. However, the AM symbiosis follows none of the constraints thought to stabilize cooperation in other well-known mutualisms and despite its significance, the mechanisms that control cooperative behavior between both partners are largely unknown. The goal of this project is to answer the following questions: (i) can fungal strains and plant hosts detect non-cooperative partners; (ii) what are the physiological mechanisms employed by partners to control the interaction and punish non-cooperators; and (iii) how does the diversity of partners influence the strength of punishment? These questions will be studied by (i) tracer experiments to determine cost to benefit ratios of cooperative and non-cooperative partners and to track resource allocation between partners under different conditions, (ii) unique 3-chamber root organ cultures to manipulate levels of defection and cooperation of partners, (iii) stable isotope probing to track carbon allocation to different partners in simulated ecosystems, and (iv) microcosm experiments to determine how plant diversity affects punishment and the fitness of different fungal strains. By studying three levels of interactions (cellular, whole plant, plant community), the different scales that stabilize cooperative behavior in the AM symbiosis will be identified. The AM symbiosis is responsible for massive amounts of global nutrient transfer in ecosystems, and plays a key role in global ecosystem stability and productivity. Investigating these processes is critical to maximizing ecosystem and agricultural benefits of the symbiosis. The project will provide training for undergraduate and graduate students, and the students will become members of an international collaborative effort and will have the opportunity to work in the laboratories of the collaborators in the Netherlands and in Canada.