施肥对高寒草甸丛枝菌根真菌群落结构及功能的影响

Arbuscular mycorrhizal (AM) fungi generaly form mutualistic symbioses with the roots of most terrestrial plants. AM fungi can increase efficiently nitrogen (N) and phosphorus (P) caputre of their hosts in return for plant carbohydrates (C); moreover, AM fungi play key roles in linking aboveground and belowground ecosystems. However, we still less understand the assembling mechanisms and ecosystem functioning of AM fungal community, and this does not facilitate our understanding in the relationship between aboveground and belowground ecosystems. Previous studies showed that N and P fertilization would change the plant community significantly, but how do the plant-associated AM fungi respond to N and P fertilization? what is the most important determinant (i.e. plant community or soil N and P availabilities) that regulates the sturcuture and function of AM fungal community? and whether the plant and soil C:N:P stoichiometry could be used as a predictor for the shifts of AM fungal community strucutre and function? These questions remain unclear.To answer the above questions, we plan to investigate how 4 yr of N and P fertilization and benomyl (kill AM fungi)treatments influence plant community, AM fungal community and soil properties/aggregation in an alpine meadow ecosystem. We aim to elucidate the influences of fertilization on the community structure and ecological functioning of AM fungi, and to illustrate the mechanism of C:N:P stoichiometry regulating the species compositions and ecosystem functioning of AM fungal community. Our research will provide new insights in the sustainable managements of alpine meadow ecosystem.

丛枝菌根（AM）真菌能与多数陆生植物根系形成基于C、N、P物质交换的互惠共生体，是地上地下生态系统相互联系的重要节点。但，目前我们对AM真菌的群落构建机制及生态系统功能仍所知甚少，严重阻碍了我们进一步理解地上地下生态系统的相互关系。前期的研究发现,N、P施肥会显著改变植物的群落结构，那么，与植物共生的AM真菌是如何响应N、P施肥？调控AM真菌群落结构及功能的关键因素是植物群落还是土壤N、P资源？植物及土壤的C:N:P计量特征能否反映AM真菌群落结构与功能的变化？针对上述问题，本项目在高寒草甸生态系统中，利用连续4年的N、P梯度施肥及杀AM真菌交互处理样地，通过分析植物群落、AM真菌群落以及土壤性质/团聚体等的响应规律，在阐明施肥对AM真菌群落结构与功能的影响机制基础上，进一步揭示植物及土壤C:N:P化学计量特征与AM真菌群落结构与功能的耦联机制，为高寒草甸生态系统的合理利用提供科学依据。

为了阐明施肥对植物共生丛枝菌根真菌（AMF）群落结构及功能的影响，本项目在高寒草甸生态系统研究了氮磷施肥对AM真菌群落结构的影响，并利用野外苯菌灵处理及室内AMF菌群接种技术探究了施肥对AM真菌群落功能的影响。研究结果表明，施N显著降低AMF侵染率，提高AMF物种多样性，改变AMF群落物种组成，同时使AMF群落功能从互惠共生向寄生发生转变；施P同样显著降低AMF侵染率，但对AMF物种多样性及群落组成无显著影响。此外，施P对AMF功能的影响在植物群落和单物种水平上有一定差异：在植物群落水平上（苯菌灵处理实验），施P使AMF对植物生物量的影响呈负效应，但对植物P营养呈正效应；在单物种水平上（垂穗披碱草AM接种实验），施P提高了AMF对植物生物量的促进作用，但却降低了AMF对植物氮磷营养的贡献。N、P混施显著降低AMF群落的物种丰富度，改变AMF群落的物种及谱系组成，而高NP肥力引起的AMF群落变化主要与越来越强的竞争排除过程相关联。本项目研究结果揭示了土壤肥力对AMF群落结构及功能具有重要的调控作用；施肥，尤其是N、P混施会造成AM真菌群落结构的巨变，会导致AM真菌群落功能从互惠共生向寄生发生转变，进而影响生态系统的可持续性。本项目相关研究结果不仅为我们科学评估和预测施肥、营养沉降等人类活动及全球变化的生态影响提供了理论依据，也为高寒草甸的草场管理提供了科学依据和技术支撑。