牦牛和藏羊践踏对高寒草甸的分异影响机制

The reasonable grazing of un-degraded alpine meadow and ecological restoration of degraded alpine meadow on the Qinghai-Tibetan Plateau are the important research topics and problems in the field of grassland science and ecology. Preliminary study of our research team found that the health status alpine meadow grazed by Tibetan sheep in recent 30 years is better than that grazed by yak in the same grazing intensity. So, a hypothesis about the harm of yak trampling to alpine meadow is more serious than that of Tibetan sheep and the trampling difference between yak and Tibetan sheep is a key reason causing grassland differentiation. However, the mechanism is not clear. So, we design a series of experiments on Tianzhu alpine meadow of Gansu Province in order to reveal the relationship between yak and Tibetan sheep grazing and trample strength, and to quantify the tramping equivalent between yak and Tibetan sheep. And systematically research the differentiation impacts of trampling yak and Tibetan sheep on alpine meadow ecosystem of "soil-grass" by simulating trampling of yak and Tibetan sheep. It will reveal the differentiation impacts and process of trampling of yak and Tibetan sheep on soil physical, chemical and biological characteristics, the dominant plants photosynthetic characteristics and storage nutrient content and reproductive characteristics, as well as the litter decomposition and soil erodibility under different grazing intnsity and rainfall. Thereby clarify the inevitability mechanism of harm of yak trampling to alpine meadow is more than that of Tibetan sheep under the same grazing intensity. In short, it will provide new ideas and bases for grazing management decisions, health management of natural grassland, restoration and maintain of degraded alpine grassland ecosystem, and grazing livestock optimization based on grassland protection.

青藏高原高寒草地合理放牧与退化草地生态修复是草学和生态领域的重要研究课题和难题。本项目组前期研究发现，相同放牧强度放牧30年藏羊的草地健康状况优于放牧牦牛的草地，提出"牦牛践踏对草地的危害重于藏羊，牦牛和藏羊践踏是造成草地分异的重要因素"，但机理尚不明确。为此，在甘肃天祝高寒草甸布控试验，揭示牦牛和藏羊践踏强度与放牧强度的关系，量化牦牛和藏羊的践踏当量。通过模拟牦牛和藏羊践踏试验，针对放牧牦牛和藏羊践踏对高寒草甸"土-草"系统的分异影响进行系统研究；揭示不同放牧强度和降雨下，牦牛和藏羊践踏对高寒草甸土壤理化和生物学性质，优势植物光合特性、贮藏营养物质含量和繁殖特性，以及调落物分解和土壤可蚀性的分异影响过程。阐明相同放牧强度下，牦牛对高寒草甸的践踏危害重于藏羊的必然性机制。为建立放牧管理决策系统、实现天然草地的健康管理以及退化高寒草地生态系统的修复和基于草地保护的草地放牧家畜优化提供依据。

青藏高原高寒草地的合理放牧与退化草地生态修复是草地生态领域的重要研究课题。基于“牦牛践踏对草地的危害重于藏羊”的假设，在甘肃天祝高寒草甸布控试验，量化牦牛和藏羊的践踏当量，研究了不同放牧强度和降雨下，牦牛和藏羊践踏对高寒草甸土壤理化和生物学性质，优势植物光合特性、贮藏营养物质含量、繁殖特性和调落物分解的分异影响过程。取得了以下重要结果或关键数据。.牦牛和藏羊的平均践踏面积分别为39.2cm2和21.6 cm2，平均蹄压分别为6.89kg•cm-2和3.13 kg•cm-2；牦牛、藏羊的平均蹄压比为2.20:1。相同的放牧强度夏季轮牧，牦牛的平均践踏强度是藏羊的1.8倍，牦牛践踏对高寒草甸造成的伤害比藏羊大。.践踏增加了表层土壤（0-15 cm）的紧实度和容重，对深层土壤无显著影响，践踏对土壤的压实效应有累积作用。践踏降低了0-10 cm草地土壤细菌、真菌和放线菌菌落数，显著降低了土壤呼吸作用。当土壤水分含量较高时，践踏对土壤的压实作用更显著。牦牛践踏对草地土壤的负面影响大于藏羊践踏。.家畜轻度践踏可促进阴山扁蓿豆的光合作用，少雨和家畜重度践踏均严重抑制了阴山扁蓿豆的生长、繁殖和光合能力。牦牛践踏对阴山扁蓿豆光合能力的抑制大于藏羊践踏，对垂穗披碱草、阴山扁蓿豆和矮生嵩草繁殖的抑制大于藏羊践踏。同等强度下，藏羊践踏处理的草层高度、总生殖枝密度及地上生物量均高于牦牛践踏处理，生殖枝死亡数低于后者。.同一放牧强度下，垂穗披碱草凋落物的损失率显著小于矮生嵩草和珠芽蓼。模拟牦牛践踏处理下的3种凋落物损失率高于模拟藏羊践踏处理。牦牛对凋落物磷含量富集的抑制作用大于藏羊。.本项目阐明了相同放牧强度下，牦牛对高寒草甸的践踏危害重于藏羊的必然性机制，从研究结果得到启示，在高寒草甸的放牧利用中适当减少牦牛比例、增加藏羊比例，可提高草地的健康程度。这为建立高寒草甸放牧管理决策系统、实现天然草地的健康管理以及退化高寒草地生态系统的修复和基于草地保护的草地放牧家畜优化提供依据。