高寒草甸嵩草与微生物竞争土壤有机氮的机制

In extremely nitrogen-limited ecosystems such as arctic tundra, boreal forest and alpine meadow, many plants showed the ability to uptake low molecular weight organic nitrogen sources, especially amino acids, from soil. Soil microorganisms are strong competitors for these organic nitrogen sources, due to their specific physiological characteristics. Niche differentiation may exist between plants and soil microorganisms in organic nitrogen uptake, which is beneficial to their mutualism and reduced nitrogen leaching from ecosystems. The Kobresia myosuroides meadow is a typical alpine meadow that covers the largest area in the Tibetan Plateau. Soil mineralization in this meadow is slow because of the low annual temperature. As a result, plant growth is strongly nitrogen-limited. On the other hand, Kobresia myosuroides have been proved to be able to directly absorb amino acids from soil. In this proposal, Kobresia myosuroides-dominated community will be used as the research subject. The differences in timing, depth and chemical form of organic nitrogen uptake by the plant and soil microorganisms will be investigated and the mechanism will be probed. The result from this research will be significant for revealing the ecological importance of plant-microorganisms competition for soil nitrogen, and for maintaining the stability and continuous development of alpine ecosystem.

在极地苔原、北方森林和高寒草甸等强烈受到氮限制的生态系统中，多种植物具有从土壤中直接吸收小分子有机氮尤其是氨基酸的能力。土壤微生物由于其独特的生理特点，是植物吸收有机氮的强有力竞争对手。植物与土壤微生物在对有机氮的获取方面可能存在着生态位分化，从而有利于两者的互利共生及减少生态系统中氮的淋失。青藏高原的嵩草草甸是最典型、面积最大、分布最广的一类高寒草甸，由于常年低温，土壤有机氮矿化缓慢，植物的生长强烈地受到氮限制；另一方面，嵩草已被证实可以直接吸收土壤中的氨基酸。本项目以嵩草群落为研究对象，探索其与土壤微生物在吸收有机氮的时间、空间和有机氮形态方面的差异及其机制。此结果对于揭示植物和微生物竞争土壤氮素的生态学意义、以及维护高寒草甸生态系统的稳定性和可持续发展具有重要意义。

青藏高原高寒草甸因常年低温，土壤有机氮矿化缓慢，无机氮供应不足，而土壤中的可溶性有机氮如氨基酸含量丰富，可能是植物氮养分的重要来源。本项目以高寒草甸中的嵩草草地为研究对象，使用稳定同位素示踪技术，主要研究了植物对土壤有机氮的吸收，以及土壤微生物对有机氮的竞争。项目自执行以来，取得以下重要结果：明确了嵩草草地的土壤理化性质和植物的氮素特征；揭示了多种植物对不同氨基酸吸收能力的差异，及其吸收受到土壤深度和季节因素的影响；阐明了土壤对外源氨基酸的吸附能力；并将揭示土壤微生物对氨基酸的竞争吸收能力。该结果对于揭示高寒草甸生态系统中植物-土壤间氮素循环的重要途径，维护该生态系统的稳定性和可持续发展性具有重要意义。