牦牛和藏羊放牧生态系统中土壤－植物界面过程及其响应机制

On the background of climate change and Anthropogenic activity, through controlling grazing trial in field which is based on yaks and tibetan sheep living in Tibetan plateau, these effects of grazing systems and intensities on soil and vegetation sub-systems of grazing ecology ecosystem including alpine meadow-yaks grazing ecosystem in Dari county which is in Three rivers region of Qinghai province, alpine rangeland-tibetan sheep grazing ecosystem in Gangcha county which located in around Qinghai lake, and process of soil-vegetation interface and their mechanism would be studied and illustrated.The study is based on the NSFC project (30960074) ,and following contents would be studied: A. Compensatory effect of different plant groups under different grazing systems and intensities; B. Differential law of ecological niche for dominant species plants and succession character of vegetation under different grazing systems and intensities; C. Changing characteritics of stoichiometric ratios of soil nutrient pool under different grazing systems and intensities; D.Carbon sequestration, soil carbon sink and source conversion under different grazing systems and intensities; E. Flora composition and quantity of soil microorganism and their changing relationship in space-time. These studied contents would provide the technical support for reasonable utilization of alpine grassland, enriche the theory of grassland grazing ecology and validate the hypothesis of optimize grazing, and answered the following scientific questions: A. how would typical plants and soil nutrient pool and microorganism coordinately change under different grazing systems and intensities? And what is their mechanism? B. How would the overgrazing result in the degradation of soil and vegetation? What would be soil carbon sink and source conversion of grassland under different grazing systems and intensities? C. What would be differential law of ecological niche for dominant species plants under different grazing systems and intensities? How would be compensatory effect of different plant groups under different grazing systems and intensities? That would not only provide the actual guidance for stability and sustainable utilization of alpine grassland grazing ecosystem, but also offered the technical support for the project of the collectivity plan for environment conservation and construction in three rive source region, and the project of the environment conservation and comprehensive control around Qinghai Lake in Qinghai province.

以青藏高原特有家畜牦牛和藏系绵羊为试验动物，通过对青海三江源区达日县高寒草甸牦牛放牧生态系统和青海湖流域刚察县高寒草原藏系绵羊放牧生态系统不同放牧制度和放牧强度下不同植物类群的补偿效应、主要优势种植物的生态位分化规律以及植被的演替特征、土壤养分库化学计量特征的变化、草地固碳量及汇/源功能转换特征、土壤微生物区系组成和数量以及时空变化关系的研究，明确放牧生态系统中土壤－植物界面过程，探讨其响应机制，最终实现为高寒草地合理利用提供技术支撑、丰富草地放牧生态学理论并验证优化放牧假设，并回答以下科学问题：①高寒草地典型植物和土壤养分库及微生物是如何随放牧制度和放牧强度协同变化的？其响应机制如何？②过度放牧是如何引起草地土壤和植被退化的？其草地碳汇/源功能转换特征如何？③不同放牧制度和放牧强度下不同草地类型主要种群生态位分化规律是什么？不同功能群植物的补偿效应如何？

本研究以青藏高原特有家畜牦牛和藏羊为试验动物，通过在高寒草地生态系统进行了不同放牧管理方式（放牧制度、放牧强度和放牧方式）对高寒草地植被和土壤特征的研究，以明确高寒草地放牧生态系统中土壤-植物界面过程，探讨其响应机制，以为高寒草地的合理利用提供科学依据。研究发现：（1）在放牧制度和放牧强度试验中，全年放牧对青藏高原高寒草地群落生物量的影响（减少）大于暖季放牧；放牧强度和群落生物量之间存在着显著的负相关，而且随着放牧强度的增加，禾草、莎草和豆科植物生物量减少，而杂类草增加；随着放牧强度的增加群落物种多样性和均匀度降低；随着放牧强度的增加，土壤种子库密度呈现先增加后降低的趋势，土壤种子库植物与地上植被之间的相似性随着放牧强度的增加而增加。（2）在放牧方式试验中，放牧第2年5个放牧处理均显著促进了群落地上净初级生产力（ANPP），而放牧第4年各放牧处理与对照相比虽然没有显著差异，但是牛羊比例1:2和羊单牧2个处理相对于对照处理有增加的趋势，且显著高于牛单牧处理，总体而言，放牧第4年ANPP高于第2年（241.9 g m-2 vs 201.0 g m-2），说明在高寒草地适度放牧（家畜采食率为50-55%），放牧有利于促进ANPP；放牧处理降低了禾草和豆科植物生物量及其在群落生物量中的比例，同时增加莎草生物量在群落生物量中的比例，而对杂类草生物量及其在群落生物量中的比例没有影响；适度放牧有利于群落主要物种的叶片功能属性向着相对生长速率增加的方向变化，因此能在一定程度上解释青藏高原高寒草地在适宜放牧率下的补偿性生长；放牧对地下生物量并无显著影响，67%-86.0%的地下生物量都集中在0-10 cm土层中，放牧第2年，牛单牧处理、牛羊比例1:2处理和牛羊比例1:4处理降低了0-10 cm土层的生物量在总生物量中的比例，而在放牧第4年各处理间无显著差异。在青藏高原高寒草地，中度放牧促使群落结构从禾草为优势变为禾草莎草为优势，并促进了植物的补偿生长，提高了生产力。