长期过度放牧下羊草胁迫记忆及其调控机制-基于光合作用的研究

Photosynthesis is the main foundation of plants to maintain the grassland ecosystem functions. Explore the mechanism of plant photosynthesis responding to long term overgrazing stress is very important to expand our understanding on the mechanism of grassland ecosystem degradation and restoration. We had found that the grassland plant has ‘overgrazing-induced stress memory’ which kept the plant at low state of photosynthesis with only 20-30% net photosynthesis rate of no-stress plants. The stressed plant keeps in this low level of photosynthesis for many years even under good growth conditions with sufficient water and nutrition supplies and no grazing pressure. However, as to now, how the plants keep this stress memory and its possible mechanism is still pending. Based on the mega-data on whole genome sequence, RNA sequence and whole-genome bisulfite sequence, we shall explore the possible mechanism of stress memory by investigating and linking the change of plant function traits, photosynthesis rates, light harvesting, carbon assimilation and expression of key function genes. The results will not only help us to explore the mechanism of grassland plant responding to over grazing stress, but also provide new knowledge for the restoration of degraded grassland and the optimization of grazing management.

光合作用是植物维持草原生态系统功能的重要基础。揭示草原植物个体光合作用对长期过度放牧胁迫的响应机制，对于理解草地生态系统退化、恢复过程和机理有重要意义。项目组前期研究表明，长期过度放牧后，草原植物个体出现低光合“胁迫记忆”，表现为其净光合效率仅为正常羊草的20-30%，即使禁牧后在水分养分充足的情况下，这种状态仍能维持较长时间。对于这种低光合放牧胁迫记忆是如何产生和维持的？我们知之甚少。本项目以内蒙古典型草原优势植物种羊草（Leymus chinensis）为对象，依托项目组开发的羊草参考基因组、转录组、全甲基化组等生物大数据，结合野外原位实验和室内分析，通过对羊草功能性状、光合特性、光反应调控与碳同化过程及相关基因调控等研究，旨在揭示基于光合作用的羊草过度放牧胁迫记忆的维持机制。预期研究成果不仅有助于阐明草原植物对过度放牧胁迫的分子响应机制，还将为退化草原恢复与放牧管理优化提供科学依据。

光合作用是植物维持草原生态系统功能的重要基础。揭示草原植物个体光合作用对长期过度放牧胁迫的响应机制，对于理解草地生态系统退化、恢复过程和机理有重要意义。通过四年的研究，我们发现，经过长期过度放牧后，羊草个体出现株高降低、叶片狭小、气孔变窄、水分利用效率降低、地上生物量降低等表型变化；与围封对照相比，放牧羊草植株叶肉细胞变小、叶绿素含量降低、Rubisco酶活性显著降低、净光合效率降低、果糖、淀粉等光合产物减少，这表明过牧羊草出现低光合胁迫记忆主要与光合碳同化过程受到抑制有关。结合基因组、全甲基化组联合分析，发现围封与放牧羊草之间存在608个差异甲基化位点，这些差异位点主要与碳水化合物代谢、激素合成、生物防御等代谢途径有关；结合转录组、全甲基化组等多组学联合分析与定量PCR分析结果，提出了羊草响应长期过度放牧的分子调控通路：“ABCCL4等气孔基因表达下调 → 气孔变窄、密度增加→水分利用率降低→光合效率降低→植株变矮”和“ILL2基因过甲基化修饰→生长素合成与信号转导通路相关基因（YUC11、SAUR、ARF7、ARF19）下调→生长素合成受阻→光合效率降低→植株变矮”。通过去甲基化试剂添加实验，发现去甲基化处理可以显著促进放牧羊草的生长，缩小放牧羊草与围封羊草之间的差距，这一结果进一步证实DNA甲基化参与放牧胁迫记忆调控。该项目研究成果不仅有助于阐明草原植物对过度放牧胁迫的分子响应机制，还将为退化草原恢复与放牧管理优化提供科学依据。