西藏高寒草原植物菌根真菌和吸收根氮获取的权衡机制研究

Roots and mycorrhizal fungi represent two alternative strategies for plants in the process of soil nutrient and water capture. Plants may choose the optimal strategy of carbon allocation and resource acquisition between the two pathways depending on the functional traits of both the root system and its associated mycorrhizal fungi. Only recently have field studies, focused on woody plants and some herbaceous species, revealed the complementarity between absorptive roots and mycorrhizal fungal in terms of resources capture. However, the carbon economy of resource acquisition through the root and mycorrhizal hyphal pathways remains unclear. In this proposed study, we plan to take advantage of nitrogen addition platform established in 2013 in Tibetan alpine steppe, aiming to explore the relationship between arbuscular mycorrhizal fungi (AM colonization, extraradical hyphal length, AM fungal biomass and community composition) and functional traits in absorptive roots (root morphology, architecture, root carbon and nitrogen concentration) of main alpine plants. Meanwhile, we will develop a novel N-15 and C-13 labeling method to quantify the nitrogen directly transferred to a host plant by AM fungi and absorptive roots and the carbon allocated to the fungi and roots by the same plant. Comparing the ratios of nitrogen benefit versus carbon cost between the root and mycorrhizal hyphal pathways would enable us to evaluate the benefit–cost changes in the belowground nutrient acquisition strategies. Results from this study would help us gain a better understanding the importance of belowground resource acquisition strategies in species coexistence and environmental adaptation mechanism of alpine plants.

吸收根及其共生的菌根真菌作为植物获取土壤资源的两个重要途径，两者之间的权衡关系决定了植物的吸收功能及其资源获取策略，对解释物种共存和多样性的维持具有重要意义。然而，菌根真菌和吸收根功能性状的变异规律及其经济学机制仍缺乏直接的定量研究。本项目以西藏典型高寒草原紫花针茅群落为研究对象，借助长期的氮添加实验平台，通过分析丛枝菌根（AM）真菌与吸收根的功能性状及其内在关系，阐明二者表观属性之间权衡关系的模式。通过根系和菌丝隔离以及N-15和C-13双标记实验，定量分析高寒植物AM真菌和吸收根的N吸收/C成本比率，揭示根系和菌根真菌在养分获取中的权衡机制，为深入理解青藏高原地区植物的生态适应机制提供重要的依据。

吸收根及其共生的菌根真菌作为植物地下部分重要的资源获取组织，定量研究二者功能性状之间的变异规律及权衡关系，既是当前植物性状研究的热点与难点，又对实现草地植物生产力优化具有重要意义。本项目围绕氮添加对高寒植物丛枝菌根（AM）真菌和吸收根功能性状及其氮吸收功能的影响，重点分析了不同施氮水平下藏北高寒草原优势植物及其主要伴生植物的菌根真菌与吸收根的功能性状及其内在关系，采用分室隔网装置结合同位素标记技术，定量分析了高寒植物菌根真菌和吸收根的氮获取能力，取得了以下主要成果：（1）分析了主要植物吸收根功能性状对氮添加的响应。发现高寒草原的主要植物根系直径较细且变异性不大，但是根系功能性状之间的相关性依然稳固，并且优势物种和伴生种表现出相反的适应策略；（2）分析了主要植物AM真菌对氮添加的响应。发现两种植物的AM真菌侵染率呈现先增加后降低的趋势，但是与根系功能性状之间未表现出权衡关系；（3）量化了菌丝和吸收根对不同植物N吸收的相对贡献。发现高氮环境下优势物种紫花针茅主要通过增强与菌根真菌的共生来获取土壤资源，而伴生种主要通过调整根系属性来提高资源获取效率。上述研究成果揭示了高寒植物适应环境能力及资源获取策略的多样性，为深入理解青藏高原地区植物群落中物种共存和多样性维持机制提供重要依据。