氮沉降影响羊草-丛枝菌根共生体适应盐碱逆境的生理机制解析

Nitrogen deposition is one of the important environmental factors affecting grassland ecosystem. Leymus chinensis is the constructive species in Songnen grassland. It has strong tolerance to salt-alkali stress, and is closely related with the symbiosis mycorrhiza. In fact, Leymus chinensis response to stress conditions is in the form of “Leymus chinensis-arbuscular mycorrhizal”. Based on the current status of atmospheric nitrogen deposition, the effect on the physiological adaptation mechanism to salt-alkali stress of Leymus chinensis - arbuscular mycorrhizal symbiont is still not clear. The project selected two kinds of arbuscular mycorrhizal fungi from the preliminary work, which have good symbiosis with Leymus chinensis and also simulated nitrogen deposition (different NH4+/NO3-) and salt-alkali stress conditions. Proteomics and metabolomics were applied to investigate the physiological and metabolic characteristics in relation to the salt-alkali tolerance of Leymus chinensis in order to reveal the effect of nitrogen deposition on the physiological adaptation mechanism of Leymus chinensis - arbuscular mycorrhizal symbiont to salt-alkali stress on the physiological level. Systems biology focuses on the salt-alkali tolerance mechanism and the ecological effect of nitrogen deposition, which is complementary to the investigations that limited in the number of physiological indicators. The results of this study not only provide a scientific basis for the use of mycorrhizal technology to enhance Leymus chinensis resistance and productivity, restoration of degraded salt-alkali grassland and biological improvement, but also provide the necessary data to support exploring the responses and feedback of Leymus chinensis and arbuscular mycorrhizae on nitrogen deposition.

氮沉降是影响草地生态系统的重要环境因子。羊草作为松嫩草地建群种，具有较强的耐盐碱性，这与共生菌根有着密切联系。事实上，羊草是以“羊草-丛枝菌根共生体”形式协同应对逆境胁迫的。基于当前大气氮沉降现状，关于其影响羊草-丛枝菌根共生体适应盐碱逆境的生理机制还并不明确。本项目以前期工作从盐碱草地中分离的与羊草共生关系较好的丛枝菌根真菌接种羊草幼苗，人工模拟氮沉降（不同NH4+/NO3-）与盐碱胁迫条件，应用蛋白质组学与代谢组学技术对羊草耐盐碱相关的生理与代谢特征进行分析，在生理学水平上揭示氮沉降影响羊草-丛枝菌根共生体适应盐碱逆境的机理。这种系统生物学的研究策略可以弥补以往研究仅“局部”考察少数生理指标的不足，深入认知羊草耐盐碱机理及氮沉降的生态效应，一方面为利用菌根技术提高羊草抗逆性与生产力，改良与恢复退化草地提供科学依据，另一方面也为探求羊草-丛枝菌根对氮沉降增加的响应和反馈提供数据支持。

氮沉降是影响草地生态系统的重要环境因子。羊草作为松嫩草地建群种，具有较强的耐盐碱性，这与共生菌根有着密切关联。事实上，羊草是以“羊草-丛枝菌根共生体”形式协同应对逆境胁迫的。基于当前大气氮沉降现状，关于其影响羊草-丛枝菌根共生体适应盐碱逆境的生理机制还并不明确。本项目通过对羊草幼苗接种摩西球囊霉（Glomus mosseae），并人工模拟氮沉降（不同NH4+/NO3-）与盐碱胁迫条件，揭示氮沉降影响羊草-丛枝菌根共生体适应盐碱逆境机理。研究结果表明，盐碱胁迫显著降低了丛枝菌根的侵染率与侵染强度，且具有高pH的碱胁迫的抑制效应更强。在各胁迫处理下，不同形态的氮素同样抑制了丛枝菌根的侵染效应，特别是在NH4+-N下，抑制更为明显。接种AMF可以显著降低盐碱胁迫下羊草叶片中Na+含量，并提高K+含量，而在氮沉降下，Na+含量有所增加，使羊草-丛枝菌根共生体对盐碱胁迫抵抗能力的下降。盐碱胁迫下接种AM真菌后共生体内的脯氨酸、可溶性糖含量无明显的积累，而在铵态氮下，两者的积累量显著高于硝态氮处理组。在盐碱胁迫条件下，接种AM使羊草体内SOD、POD、CAT 和APX的活性明显提高，增强宿主植物体内氧自由基的清除能力。而在氮沉降，特别是NH4+-N下，各种抗氧化酶活性显著降低。另外，接种AMF对羊草幼苗适应盐胁迫过程中蛋白质组与代谢组均发生了变化，提高了羊草幼苗的抗盐性。本项研究对于深入认知羊草耐盐碱机理及氮沉降的生态效应提供了理论依据，一方面为利用菌根技术提高羊草抗逆性与生产力，改良与恢复退化草地提供科学依据，另一方面也为探求羊草-丛枝菌根对氮沉降增加的响应和反馈提供数据支持。