不同氮磷肥力下丛枝菌根介导的土壤碳固持研究

Arbuscular mycorrhizal (AM) fungi generally form mutualistic symbioses with the roots of most land plants. Plants supply AM fungi with carbohydrates, and in return, fungi increase efficiently nitrogen (N) and phosphorus (P) caputre of their hosts; moreover, AM fungi play key roles in linking aboveground and belowground ecosystems. It has been well accepted that AM fungi are one of the important components of soil organic carbon (C), and also that these fungi play key roles in regulating soil C sequestration. However, how the AM fungi mediate soil C sequestration and whether soil N and P fertility will influence the AM fungi-mediated C sequestration, are still poorly understood.To answer these questions, we plan to investigate how 5 yr of N and P fertilization treatments influence the AM fungi-mediated C sequestration in an alpine meadow ecosystem with multiple state-of-the-art techniques, including the installation of hyphal in-growth bag in field,mesocosm inoculation experiment,454 sequencing and the measurement of phospholipid fatty acid. We aim to elucidate the underlying mechanism of AM fungi-mediated soil C sequestration, and to illustrate how soil N and P fertility influence the process of AM fungi-mediated soil C sequestration. Our research will provide new insights in the understanding of AM fungal function and soil C sequestration,and will also facilitate our prediction in the ecological impacts of N and P depositions.

丛枝菌根（AM）真菌能与多数植物根系形成基于C、N、P物质交换的互惠共生体，是地上地下生态系统的重要联系节点。已有研究表明，AM真菌是土壤有机C库的重要组成部分，在影响和驱动土壤C固持过程中扮演了关键性角色。然而，AM真菌是如何介导土壤C固持过程？该过程是否受土壤N、P养分的调控？这些问题迄今仍未得到科学的回答。针对上述问题，本项目在高寒草甸生态系统中，利用连续5年的氮、磷梯度施肥样地，通过定位埋设菌丝生长袋及AM真菌群落接种实验，结合454高通量测序、磷脂脂肪酸分析等技术手段，在阐明实验处理对AM真菌群落结构、AM真菌C储量、土壤有机C、植物群落等的影响规律基础上，进一步揭示高寒草甸生态系统中AM真菌介导的土壤C固持机制及其对N、P肥力的响应。本项目预期研究结果将丰富我们对菌根生态系统功能的理解，拓宽土壤C固持/循环的研究思路，为预测和解决N、P沉积等引起的生态环境变化后果提供科学依据。

丛枝菌根（AM）真菌能与植物根系形成互惠共生体，在促进植物生长及调控C循环等方面具有重要作用。为了阐明不同土壤肥力下AM真菌对土壤C固持的影响，本项目在高寒草甸生态系统中研究了氮磷施肥对菌丝生长袋内AM真菌C储量的影响，并结合野外苯菌灵抑制菌根处理及温室菌根接种技术研究了施肥对AM真菌介导的土壤C固持的影响机制。结果表明，菌丝生长袋内AM真菌的C储量平均为0.54 mg C g-1土，占土壤有机C库的2.73%；氮磷混施对菌袋内AM真菌C储量无明显影响，却降低了土壤有机C库中AM真菌C的占比；氮磷混施降低了菌袋内AM真菌的物种丰富度及改变了AM真菌的物种组成，且AM真菌的物种组成与土壤净C固持率相关联；此外，施N对菌袋内AM真菌介导的凋落物降解及C循环相关酶活（β-葡糖苷酶、纤维二糖水解酶和N-乙酰-葡萄糖苷酶）均无显著影响。在野外情况下，抑制AM真菌（苯菌灵处理）提高了植物的生物量，但同时降低了土壤有机C含量；施N和苯菌灵处理对植物生物量及土壤有机C含量均无显著的交互影响效应。在温室菌根接种实验中，不同土壤氮磷肥力能影响AM真菌介导的植物碳同化；在低肥条件下，AM真菌的存在不利于土壤有机C固持，但在高肥条件下，尤其是P充足的情况下，AM真菌有利于土壤有机C固持。上述研究结果丰富了我们对AM真菌生态系统功能的理解，为预测营养沉降引起的环境变化后果提供了科学依据。

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