基于植物功能性状揭示荒漠草原不同放牧退化演替过程中的群落构建机制

Understanding how environmental factors and human activity drive plant community assembly remains a major challenge in community ecology. Two opposing processes, namely deterministic environmental filtering and nondeterministic elements such as interspecies competition, can be quantified by analyzing trait distributions in the community-assembly process. This study was carried out in the Inner Mongolia desert grassland. Combined with long-term vegetation survey, laboratory experiment and constantly monitering of climatic factors. The plant functional traits, several ecosystem functions such as species diversity, functional diversity, productivity, and several environmental factors included climatic and soil elements were acquired. This study could clarify the relationship between different plant functional traits, and the response of plant functional traits to grazing gradient. It was also helpful to reveal the response of species diversity and functional diveristy to long-term different grazing intensity. Furthermore, based on the understanding of species coexistance machanism under the long-term interference of different grazing gradient by the plant functional traits, it could explore the relative contributions of two processes in community assembly, the environmental filtering and interspecies competition, and their relationships with grazing intensity. The study is expected to enrich the theory study of grassland biodiversity. It also provided scientific support for guidance of desert grassland restoration and biodiversity conservation.

放牧退化演替下的草地物种多样性的形成与维持机制，即群落构建的成因，一直是草地生态学关注的核心论题。本研究以内蒙古荒漠草原为研究对象，结合长期固定监测样地植被调查、室内实验以及长期气候因子监测获得长期不同放牧强度下的植物功能性状、物种多样性、功能多样性、生产力以及气候、土壤等环境因子指标，从而阐明不同植物功能性状之间的相互关系以及不同植物功能性状对放牧的响应；揭示荒漠草原物种多样性对长期不同强度放牧干扰的响应机制；并从植物功能性状的角度进一步明确长期不同强度放牧干扰下群落物种共存机制的基础上，探究群落构建的两种作用机制，即环境筛选和种间竞争，在群落构建中的相对贡献与放牧强度之间关系及维持机制。在丰富草地生物多样性研究理论的同时，为荒漠草原等脆弱生态系统恢复和生物多样性保护提供科学依据。

本项目以内蒙古农业大学荒漠草原放牧试验样地为研究对象，结合放牧强度、放牧年限（2004-至今）、气候、土壤等影响因子，分析荒漠草原群落在4种放牧干扰强度（无放牧、轻度放牧、中度放牧、重度放牧）下的群落构建机制。采用两步零假设模型定义群落构建过程，详细阐述长期气候因子和放牧干扰共同作用下的植物功能性状分布范围及其分布格局及与放牧强度和放牧年限的关系，从而揭示不同放牧干扰下荒漠草原的群落构建过程，探讨荒漠草原对长期放牧活动的适应机理。结果发现：（1）在长期不同放牧强度下群落物种组成不断发生变化，且随着放牧年限的增加群落中出现了更多资源利用率高、竞争能力强的物种，且放牧强度越高，这种现象越明显；（2）物种多样性在4个放牧处理之间没有差异，但功能多样性随着放牧强度逐渐减小；（3）物种多样性随着放牧年限没有明显的趋势变化，而控制区和轻度放牧区功能多样性随年份的变化具有显著增加趋势；（4）环境筛选随年份具有显著变化的区域多数分布在放牧强度较高的样地（中度和重度），且大部分功能性状分布范围是逐年减小的。可见，在放牧强度较高的区域，环境条件更加贫瘠，对物种的筛选作用更加强烈；（5）部分植物功能性状的分布格局随着年份具有显著的从聚集转变为发散的趋势。表明，随着年份的增加，物种对资源的竞争逐年增加，物种之间的生态位越来越分化。综上，物种之间对资源的竞争及其生态位分化是荒漠草原群落适应长期高强度放牧干扰的主要策略。本研究将在丰富草地生态系统群落构建研究理论的同时，为荒漠草原等脆弱生态系统恢复和生物多样性保护提供科学依据。