青藏高原多年冻土植物群落对模拟增温与放牧的响应变化

The Qinghai-Tibetan Plateau is highest in elevation between middle and low latitudes. It is the largest permafrost area in the world with covering an area of about 1.5 million km2. It is one of the world most extremely sensitive areas to climate change. Climate warming causes permafrost melting, evaporation of soil moisture, and violent change in soil organic carbon. Consequently, it continues to release large amount of greenhouse gases and intensifies global warming. Therefore, the Qinghai-Tibetan Plateau becomes an interesting area for international research. Studies in permafrost and arctic area showed that alpine meadow in low temperature is very sensitive to climate change. As a consequence, soil water and nutrition changes significantly, subsequently affects interspecies competition and community structure and finally leads to an important impact to ecosystems. Vegetation coverage plays a very important role in the insulation regulating heat transfer in the permafrost layer. Therefore, it is important to study permafrost vegetation response to climate change. It is a key to predict the effect of future climate warming and human activities to alpine permafrost grassland ecosystem and its succession direction. Currently, studies about the effects of climate warming and human activities on plant community and ecosystem are focused on modeling, gradient change of natural environment, and meta analyses. Most of them aim at the community composition and structure and few studies focuses on the alpine ecosystem. Furthermore, there is a shortage of controlled experiments analyzing climate change and grazing on permafrost ecosystem. In this study, we used experimental warming to simulate global warming and cutting to simulate grazing, studying the response of plant community in the permafrost zone alpine meadow, verifying the following scientific assumptions: ① Warming and grazing disturbance will cause changes of morphological characteristics of individual plants firstly, different species has different change, which will alter community structure via change the interspecies relationships and species competition; ② Warming will improve growth of plants and increase soil organic matter, and accelerate its decomposition. The two parts of change will be offset in an extent, which will cause soil carbon pool tends to stable. The purpose of this research is to study the plants responses from individual plants, population, functional groups and soil environment, to clarify the effect mechanisms of climate change and grazing disturbance on plant community and soil carbon in permafrost alpine meadow, to more scientifically and accurately predict the effects of future climate change and human activities on permafrost alpine meadow ecosystem and its trend of succession.

多年冻土区植被覆盖对冻土层热量传递有着非常重要的隔绝和调节作用，而气候变暖和人类活动使该区植被发生退化演替，并致使冻土融化释放大量温室气体加速全球变暖。本研究以模拟增温与放牧为环境变化和干扰因子，研究冻土区高寒草甸植物群落的响应变化，验证以下科学假设：①温度升高和放牧干扰会使植物个体形态、生长繁殖特性发生改变，且不同物种的变化存在差异性，这种差异性会通过改变种间关系和种间竞争而使群落发生演替；②温度升高会促进冻土植物生长，并使土壤有机质增加；同时温度升高又会加速土壤有机质的分解，二者会在一定程度上抵消土壤碳的变化量而使土壤碳库趋于稳定。目的是从组成群落的植物个体、种群、功能群以及土壤环境等不同水平和角度研究植物的响应，弄清气候变化和放牧干扰对冻土高寒草甸植物群落和土壤碳的影响机理，更加科学和准确地预测未来气候变化和人类活动对冻土高寒草甸生态系统的影响及其演替趋势。

青藏高原被誉为地球“第三极”，分布着大面积的多年冻土，是全球变化的敏感区域。当前的气候变暖和高强度人类活动造成的多年冻土融化和高寒生态系统退化，已对当地的生态安全和牧业生产造成严重威胁。高寒草甸是青藏高原主要的生态系统类型之一，且大部分分布于多年冻土区。目前关于气候变化和放牧活动对该区域高寒草甸植物群落结构及其生产力影响的研究较少，而且研究结果有较大的不确定性。研究冻土区高寒草甸植物群落组成结构及其生产力对气候变化和放牧的响应及其机理，对于预测未来气候变化和人类活动对高寒生态系统和冻土区域环境的影响具有重要意义。.本研究在青藏高原多年冻土区高寒草甸上以模拟增温与刈割分别作为气候变化和人类干扰因子，实验设计对照（Ck）、刈割（Clipping）、增温（Warming）、刈割+增温（ClW）共4个处理。采用红外辐射仪模拟增温约2℃，以刈割模拟秋季放牧，测定分析了实验过程中土壤温湿度、土壤化学性质、群落组成与结构、地上生物量、植物叶片性状以及物候特征等指标的响应变化，探讨了增温和刈割条件下群落结构组成和生产力与土壤特性、降雨量、植物形态特征和物候期变化的关系。结果表明，6年的模拟增温与刈割对多年冻土区高寒草甸植物群落物种组成与结构无显著影响，但模拟增温增加了群落地上生产力，刈割对群落生产力的影响不显著，高寒草甸生产力在物种、功能群和群落水平上对增温和刈割的响应不同。模拟增温改变了高寒草甸植物的物候期。这些结论有助于我们更好地认识冻土高寒生态系统对未来气候变化和人类放牧活动的响应机制及其与环境变化之间的反馈，并为青藏高原地区的生态保护和牧业生产管理提供理论依据。