青藏高原高寒草甸冷季牧场精准休牧期的确定及其生态学机理

Grazing rest is an important measure of grassland management, which has become one of the effective measures for ecological restoration and reconstruction of currently degraded grassland. It is generally known that the grazing rest period of alpine meadow on Qinghai-Tibetan Plateau should started at forage turning green stage. However, at the stage of soil ablation, the negative effects of livestock trampling on grassland are very serious as livestock trampling will tear away the sod from the grassland or form a "hoof hole" as well as damaged plant underground tissue severely. So, the scientific hypothesis of this program is that the grazing rest of alpine meadow should started before soil thawing. Therefore, the effects of grazing rest begin at the stage before soil thawing, initial stage of soil thawing, mid period of soil thawing, and at beginning of forage turning green period on "soil-grass" system in Gansu Tianzhu alpine meadow were studied, compared with traditional grazing rest. The objectives of this study were to clarify the effects of different grazing rest periods on soil physical properties, chemical properties and biological properties of alpine meadow, and reveal the effects of different grazing rest periods on the reproductive characteristics, grassland plant community characteristics, photosynthetic characteristics and plant productivity of alpine meadow on the Qinghai-Tibetan Plateau. So, the precise grazing rest period of alpine meadow and its ecological mechanism was determined, and the inevitable mechanism of optimal grazing rest period of cold pasture on alpine meadow should started before soil thawing was clarified. It can provide the basis for establishing grazing management decision system, realizing the health management of natural grassland, repairing degraded alpine grassland ecosystem and grassland grazing optimization management based on grassland protection.

休牧是草地管理的一项重要措施。众所周知，青藏高原高寒草甸冷季牧场休牧应始于牧草返青。然而，高寒草甸土壤解冻期，家畜践踏对草地的破坏非常严重，常引起解冻的草皮从草地剥离或形成“蹄坑”，损伤植物地下组织。基于高寒草甸冷季牧场休牧应在土壤解冻前进行的科学假设，在甘肃天祝高寒草甸布控试验，以当地传统休牧为对照，研究冷季牧场土壤解冻前、土壤解冻初期、土壤解冻中期、牧草返青初期开始休牧对高寒草甸“土-草”系统的影响，明晰不同时期休牧对高寒草甸土壤物理性质、化学性质和生物学性质的影响，揭示不同时期休牧对高寒草甸优势植物的繁殖特性和光合特性、草地植物群落特征影响；进而明晰青藏高原高寒草甸冷季牧场的精准休牧期及其生态学机理，阐明高寒草甸冷季牧场休牧应在土壤解冻前进行的必然机理。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优化管理提供依据。

探究最佳春季休牧时期对高寒草甸的精准休牧管理及进行可持续利用具有重要意义。本项目针对土壤解冻和牧草返青等关键时期，设置不同的休牧开始时间：1）土壤解冻临界期－牧草枯黄期（R1），2）土壤解冻后期－牧草枯黄期（R2），3）牧草返青初期－牧草枯黄期（R3），4）牧草返青后期－牧草枯黄期（R4），5）传统休牧期－牧草枯黄期（R5）（对照），研究了不同时期休牧对高寒草甸“土-草”系统的影响。结果表明，R1有利于高寒草甸植被和土壤恢复。在草地生产力方面，R1（306.48 g•m-2）>R2（276.90 g•m-2）>R3（249.45 g•m-2）>R4（231.26 g•m-2）>R5（188.66 g•m-2）。较R5相比，R1显著提高了植物高度、盖度、植物群落Margalef丰富度指数、Shannon-wiener指数和Pielou均匀度指数。随着休牧期的提前，植物有性繁殖效力（SRE）增加，营养繁殖效力（VRE）降低。植物根系在R4和R5中受损害程度最大，产生较高含量的脯氨酸、丙二醛含量和超氧阴离子自由基。休牧4年后，植物的根系贮藏物质随着休牧期提前而增加。土壤种子库密度随着休牧时期的提前而增加，其中以R1土壤种子库密度最高，对草地植物群落的恢复潜力最大。较R5相比，R1显著增加了土壤水分、速效磷、硝态氮、有机质、有机碳、易氧化碳、可溶性碳、土壤大团聚体（2-5 mm）含量及细菌多样性；牧草返青后继续放牧降低表层土壤有机碳含量和稳定性，以R5的土壤有机碳含量和易降解碳含量最低。综合分析认为，高寒草甸在土壤解冻临界期开始春季休牧能够显著提升草地生产力，保护植被和草皮免遭践踏破坏，促进植被和土壤恢复，可实现草地有效利用和生态保护兼并的目的。