氮素对丛枝菌根真菌群落结构及共生效能的影响及作用机制研究

Arbuscular mycorrhizal fungi can form symbiotic association with the majority of terrestrial plants and have important ecological and physiological functions, such as helping host plant to acquire mineral nutrients including nitrogen (N) and phosphorus (P), enhancing plant tolerance to various biotic and abiotic stresses; stabilizing the ecosystem structure and functions and intensifying the ecosystem resilience to environmental changes. On the other hand, nitrogen (N) plays a key role in predicting the primary productivity of terrestrial ecosystems. In recent years, more and more N has been introduced into terrestrial ecosystems due to increased application of N fertilizer and N deposition, which may increase the productivity of the N-limited ecosystems, while excessive N input may also generate negative impacts on the ecosystem. Previous studies have shown that soil N content may have critical influences on the structure of AM fungal community, however, the effects of N levels on mycorrhizal symbiotic effectiveness rarely have been studied. More importantly, there is a lack of systematic and in-depth study of the mechanism underlying the N effect on AM fungal communities. Based on the long-term field experiment investigating the impacts of N deposition on the typical steppe ecosystem in Inner Mongolia, the proposed project will comprehensively study the effects of soil N levels on the AM fungal community structure. Series of microcosm experiments will be carried out to reveal the impacts of N on eco-physiological functions of the AM symbiosis, and also to uncover the underlying mechanisms. The study is expected to better the understanding of the ecological impacts of N input to terrestrial ecosystems and provide support to sustainable management of N in natural ecosystems, and also support to protection of AM fungal resources.

丛枝菌根（AM）真菌能够与大多数陆地植物形成互惠共生体系，具有重要的生态生理功能，包括帮助植物获取矿质养分，增强植物对各种逆境胁迫的适应能力，在环境变化背景下稳定生态系统结构和功能等。氮素是陆地生态系统初级生产力的关键限制因子，近年来由于大量施用氮肥及氮沉降的增加，越来越多的氮素进入陆地生态系统，这一方面有可能提高受氮限制的生态系统的生产力，但过多的氮素输入也可能产生负面的生态环境效应。已有研究表明，土壤氮含量对AM真菌群落结构可能具有重要影响，但对于氮素水平是否影响菌根共生效能缺乏了解，对于氮素影响AM真菌群落的机理更缺少系统深入的研究。本项目基于内蒙古草原生态系统氮沉降试验平台，结合系列模拟生物学试验，从生态生理到分子层面，全面揭示氮素对AM真菌群落结构和共生效能的影响及其作用机制，从而推进对陆地生态系统氮素输入生态效应的深入认识，为生态系统氮素管理和菌根真菌资源保护提供科学依据。

氮素是植物所必需的矿质养分，也是陆地初级生产力和生态系统功能的重要限制因素。大规模的氮肥生产和施用导致全球范围内氮沉降的增加，对自然生态系统的生物多样性和稳定性带来巨大威胁。丛枝菌根 (AM) 真菌与绝大多数陆地植物形成共生体，帮助植物获取矿质养分，影响生态系统功能和稳定性，探究AM真菌群落对氮沉降的响应有助于我们客观全面地认识氮沉降的生态效应，制定科学的应对策略。本项目依托内蒙古典型草原长期氮沉降定位试验，设置0 - 50 g N m-2 y-1 9个氮输入水平，采用高通量测序手段研究土壤AM真菌群落对氮沉降的响应。结果表明：当氮沉降速率低于20 g N m-2 y-1时，AM真菌群落多样性保持稳定，超过这个氮水平后AM真菌多样性急剧降低，而AM真菌生物量随氮沉降速率的升高持续降低，与多样性响应呈现明显的不一致性。氮沉降还显著改变了AM真菌的群落组成，表现为不同AM真菌属对氮沉降的不同响应。结构方程模型 (SEM)分析表明：土壤有效氮和N:P为低氮水平下影响AM真菌群落的主要因素，土壤pH则为高氮下影响AM真菌群落的主要因素。共现性网络分析进一步表明：高氮速率降低了AM真菌群落稳定性，且群落稳定性与多样性呈显著正相关。此外，通过盆栽控制试验探究了氮素添加对AM共生效能的影响，发现施氮促进了菌根共生，显著增加了植物对氮素的吸收，同时降低了土壤pH；接种AM真菌促进了植物养分吸收，但总体降低了植物生物量。本研究揭示了AM真菌群落结构对氮素输入的响应特征和机制，以及氮沉降背景下AM真菌对典型草原优势禾草生长发育和养分利用的影响，研究结果为全面认识草原生态系统对全球变化的响应及制定应对策略提供了科学依据。