冷蒿根系分泌物对根际微环境的调控及其与耐牧关系

Grassland degradation is the main ecological problem in the Northern part of China. With the support of National Natural Science Foundation of China, we have finished a lot of research on the mechanism of tolerance to grazing in the aboveground parts of Artemisia frigida Willd. The volatile organic compounds (VOCs) from the stems and leaves of A. frigida mainly include eucalyptol, α-terpineol, camphor, etc., which markedly inhibite the seed germination and seedling growth of local pasture grasses, and plays an important role in the tolerance to the livestock feeding. The extracts of A. frigida roots, which contain the same compounds with the VOCs, also have the inhibition to the pasture grass growth. In this project, in order to further reveal the relationship between the root growth metabolism system and the tolerance to grazing in A. frigida, we will compare the difference of exudates from A. frigida roots under different grazing pressure, and study the interaction and regulation of root exudates and rhizosphere soil nutrient, soil enzyme activity, soil microorganism from field and laboratory experiments. Meanwhile, the contribution of the rhizosphere microenvironment to the ability of tolerance to grazing in A. frigida will be demonstrated by the studies of root growth, physiology and biochemistry metabolism, and the expression of genes related to the metabolism. The above results expect to reveal the mechanism of physiology, biochemistry and molecular for tolerance to grazing of A. frigida, and furtherly provide clues for the study of the underground ecology in Grassland.

草地退化是我国北方面临的主要生态问题。申请人在国家自然科学基金资助下，对冷蒿地上部分耐牧生存机制开展了大量的研究工作。冷蒿枝叶释放VOCs（桉树脑、α-萜品醇和樟脑等）对伴生牧草种子萌发和幼苗生长具有显著的抑制作用，对家畜采食具有防御作用；冷蒿根系浸提液中含有VOCs相同的化合物，对伴生牧草生长也具有抑制作用。为了进一步研究冷蒿地下根系生长代谢系统与耐牧的关系。本项目拟以冷蒿根系释放分泌物入手，寻找放牧压力下冷蒿根系释放分泌物的差异，并分别通过野外和室内试验研究这些根系分泌物与根际土壤养分、土壤酶活性和土壤微生物变化的互相调控关系。同时通过研究冷蒿根系生长、生理生化代谢以及代谢相关基因表达等指标，明确根际微环境变化对冷蒿耐牧能力的贡献。研究结果将揭示冷蒿耐牧的生理生化和分子机理，为草地地下生态学的研究提供借鉴。

冷蒿（Artemisia frigida）在草原植物群落中具有非常特殊的行为，它伴随着草场退化演替的各个阶段，是群落演替过程显著标志植物之一。为了探讨冷蒿根系次生代谢物与根际土壤养分和土壤微生物的关系，以及根际微环境变化对冷蒿耐牧能力的贡献。本研究采用野外和室内试验、人工模拟和控制放牧相结合的方法，进行了冷蒿次生代谢产物、非结构性碳、膜脂脂肪酸含量、抗氧化酶活性和LOX活性的研究，以及冷蒿根际土壤营养元素、土壤酶活性和土壤微生物群落多样性的研究。结果表明：机械损伤导致冷蒿枝叶中游离态和结合态酚酸总量增加，根系中结合态酚酸减少，诱导体内应激防御系统酚酸合成关键酶活性升高，促进抗氧化物质酚酸的积累，调节冷蒿体内木质素合成以及醌类和单宁形成；机械损伤冷蒿体内淀粉、蔗糖、葡萄糖质量分数发生变化，参加应急反应，同时轻度损伤可以增加冷蒿体内非结构性碳水化合物；机械损伤冷蒿细胞膜系统被破坏、LOX活性升高、体内ROS含量升高，促使快速、有效启动体内抗氧化防御系统，清除体内过量的ROS，维持一定的AsA-GSH循环效率。轻度放牧使冷蒿根际土壤酶活性和微生物数量显著增加，改善土壤微生态环境；重度放牧冷蒿能够改变土壤pH值，促进有机质的分解，提高土壤有效养分及有效微量元素的含量，而土壤微生物数量减少，酶活性降低；放牧能够降低土壤微生物群落多样性，冷蒿根际能够提高土壤微生物群落多样性，改善土壤微生态，进而促进冷蒿生长。该成果为进一步揭示放牧对草场植物生长的作用机制，以及阐明冷蒿耐牧的生理生化和分子机理和构建草场植被恢复技术提供理论依据。