放牧制度和放牧方式对高寒草原土壤及植被更新影响的研究

The stability of alpine ecosystem is important for ecological function on climate stabilization, water source conservation, soil conversation, biodiversity and carbon sink, productive function on animal production and livehood function on herdsmen in the region of Tibetan Plateau. Grazing has been the main land-use method on the alpine grassland, which makes the rational grazing management to be the basis of the sustainable development of animal husbandry and maintenance of ecological security function in the Tibetan Plateau. In this work, the controlled experiments with grazing system, grazing intensity, and grazing mode will be set to study the influence of grazing on the temporal and spatial dynamics of soil nutrients, soil microbes, soil seed bank and vegetation regeneration. We are about to explore the interaction between grazing and soil of alpine grassland ecosystem, then provide information for rational utilization of the alpine grassland resources, enrich grazing ecology theory. Through the work, the following scientific questions will be answered: (1) Do grazing systems or grazing modes, or the both relate to the degradation of alpine grassland soil? If so, what is the degradation mechanism? (2) Do the temporal and spatial dynamics of microbes indicate the healthy situation of the grassland ecosystem under different grazing systems, grazing intensity and grazing mode? Could these dynamics be regarded as the warning signal for unsuitable grazing activities? 3) Which species’ or functional groups’ seed bank are the decisive factors for the development of the alpine grassland ecosystem under different grazing systems, grazing intensity and grazing mode?

青藏高原高寒生态系统的稳定直接关系到该地区气候维持、水源涵养、生物多样性和碳汇功能等生态功能、畜牧业生产功能以及当地农牧民群众的生活功能，而放牧利用依然是目前高寒草地的主要利用方式，因此科学合理的放牧管理是保障青藏高原高寒牧区“生产-生态-生活”三大功能的基础。本项目拟通过高寒草原地下养分库化学计量特征、土壤微生物、土壤种子库的动态变化及植被更新对不同放牧制度和放牧方式的响应及其机制研究，探讨该地区高寒草原科学合理利用的有效途径，丰富草地放牧生态学理论，拟回答以下科学问题：（1）放牧制度或放牧方式、还是二者同时引起高寒草原土壤的退化？其机理如何？（2）不同放牧制度和放牧方式下高寒草原土壤微生物时空动态变化如何表征高寒草原放牧系统当前的状况，并凭此对草地放牧方式及强度做出预警？（3）哪些物种/功能群的种子库变化对不同放牧制度和放牧强度及不同放牧方式下高寒草原植被更新具有决定作用？

本项目以2个典型的高寒草地放牧生态系统为研究对象，探讨了放牧强度和放牧方式对“土壤-草地-家畜”的影响及其机制，为优化高寒草地放牧管理方式，实现高寒草地适应性管理和草地畜牧业可持续发展提供数据支持和理论依据。研究发现：（1）在紫花针茅高寒草原，放牧显著增加了紫花针茅高寒草原各土壤种子库的物种丰富度和密度，随着放牧强度的增加，物种丰富度呈现先上升后下降再上升的趋势，种子库密度则呈现不同的响应趋势。轻度放牧有助于增加大种子物种的丰富度和密度，重度放牧则有助于增加小种子物种的丰富度和密度。（2）在草甸化草原，牦牛放牧增加土壤全碳含量而降低全磷含量，藏羊放牧则降低土壤全碳含量而增加全磷含量；混合放牧对土壤微生物群落结构的影响更大，而且放牧对土壤真菌群落影响更显著；土壤节肢动物以螨总科和甲螨总科为优势类群，主要分布于0~5 cm土壤层，其群落组成和数量具有明显的季节动态，就放牧的影响而言，藏羊放牧增加了土壤节肢动物密度、群落组成以及多样性；牦牛藏羊混合放牧有利于维持较高的群落多样性和生产力，同时提高了家畜对草地资源的利用，增加了采食量和对牧草的表观消化率，有利于家畜增重。（3）综合植物和家畜的响应，初步确定草甸化草原适宜的家畜组合为牦牛和藏羊1:2混合放牧。