典型草原植物多样性对放牧和环境因子波动的响应与机制

The current project is planning to investigate the response patterns, processes and underpinning mechanisms of typical steppe community structure and diversity to different grazing intensity and different type of grazers through controlled field experiments in Inner Mongolia. Based on a long-term manipulated sheep grazing trial which was established and maintained by Inner Mongolian grassland ecosystem research station and a newly designed cattle and cattle & sheep mixed experiment, we plan to simultaneously and continuously measure plant community structure, plant functional traits, forage quality and diet selection of grazing animals. By integrating these data with the data set that has been obtained from the past, we plan to explore the thresholds and trajectories of the responses of plant species diversity, functional diversity, and phylogenetic diversity to grazing intensity and climatic fluctuations; to discover the potential mechanism that are accountting for the diet selection of different grazing animals; to examine the divergent and convergent responses of plant community structure to different grazers; to study the mechanisms of plant species coexistence and dominance under different types of grazing. In order to provide scientific basis for guiding biodiversity conservation and sustainable grassland management practices.

本项目计划以内蒙古典型草原为研究对象，通过控制实验的手段，研究和揭示典型草原植物群落结构和多样性在不同强度和方式放牧干扰下的响应格局和适应机制。利用内蒙古草原生态系统国家野外科学观测研究站建立的长期绵羊放牧实验平台，并新增设放牛和牛羊混牧实验，通过对植物功能性状、植物群落结构、牧草品质和食草动物选择性采食等指标的连续观测与研究，结合已有的数据和成果积累，揭示典型草原植物多样性（包括物种多样性、功能多样性和谱系多样性）对于长期放牧响应的阈值和变化轨迹；探索牛羊选择性采食的潜在机制；比对不同放牧干扰下群落结构响应的趋同和分异；解析典型草原群落植物物种在放牧干扰下的优势转换和共存机制；为指导我国草地生物多样性保育，草地可持续利用提供科学依据。

本项目通过两个历史实验平台积累数据，和一个新增模拟放牧实验平台，对食草动物选择性及非选择性采食作用在草地群落结构中的作用和机制进行了研究。研究发现：1）适口性较好的植物，主要是杂类草，在中度放牧强度水平收到的负面影响最为严重，由于这些物种对于整个植物群落物种多样性的具有重要贡献，因此放牧强度与多样性呈U形曲线关系，与之相反，地上生物量和物种组成空间异质性与放牧强度呈凸型曲线关系；2）冷季降水对在群落中占主导地位的C3植物丰度正相关，而与杂类草和C4植物的丰度负相关，冷季降水增高因此对群落物多样性具有显著地负面影响； 3）相对于绵羊的选择性采食作用，非选择性采食因对优势物种具有明显的抑制作用，其作用与选择性采食和氮沉降对于物种多样性作用恰好相反，显著提高了群落的物种多样性。这些发现对广泛接受的中度干扰假说进行了实验检验，并证明了食草动物的采食的选择性、降雨的季节分布及氮沉降对于草原群落结构的维持具有十分重要的作用，是未来草原生物多样性保护和可持续利用亟待考虑的关键因素。