三江源退化高寒草地土壤碳汇对植物功能群时空变异的响应机制

Alpine grassland in the Yellow River, Yangtze River and Lancangjiang River, Qinghai Province, China ecological environment is fragile, sensitive to climate change and ecological function is important. Alpine grassland carbon pool function and regional carbon balance have important position. Under the effect of environmental factors and human disturbance, alpine grassland degeneration was extensive and serious, and structure and function of Grassland plant functional groups changed, and caused the soil carbon sink changed. Alpine grassland carbon balance destroyed even feedback to the terrestrial ecosystem carbon balance. Therefore, in this study, alpine grasslands in source area of three major rivers of China were selected as research area because they have certain scientific research foundation. Through field observation and indoor measurement, analyze and illustrate plant functional groups quantitative and functional characteristics of spatial and temporal variation pattern in the alpine grassland different degradation succession stages and soil carbon pool to its response mechanism. They have important scientific significance to answer some questions under the background of climate change in the future. For example, what kind of spatial and temporal variation will happen that alpine grassland degradation succession leads to plant functional groups structure and function, what change that carbon input and output mechanism of plant functional groups, and then what kind of impact on soil carbon sink, soil carbon input and output changing correspond to structure and function threshold of plant functional groups. Also for alpine grassland vegetation restoration and reconstruction, reducing greenhouse gas emissions to provide scientific basis.

三江源区高寒草地生态环境脆弱、对气候变化敏感、生态作用重要。高寒草地的碳库作用及在区域碳收支平衡中占有重要地位。在环境因素和人为扰动共同作用下，高寒草地退化广泛且严峻，草地植物功能群结构及功能发生变异，引起土壤碳汇变化，破坏了高寒草地碳的收支平衡甚至反馈到陆地生态系统的碳平衡。因此，以具有一定科研基础的青海三江源核心区高寒草地为研究区，通过野外观测、室内测定等，分析和阐明高寒草地不同退化演替阶段植物功能群数量特征和生态功能特征的时空变异规律以及土壤碳汇对其的响应机制，对于回答在未来气候变化背景下，高寒草地退化演替导致植物功能群结构和功能发生怎样的时空变异，植物功能群碳输入输出机制发生怎样的改变，进而对土壤碳汇产生怎样的影响，土壤碳收支发生转变时对应的植物功能群结构与功能阈值等关键科学问题具有重要科学意义，也为高寒退化草地植被恢复与重建、减轻高寒草地温室气体排放提供科学依据。

三江源区高寒草地生态作用重要，高寒草地的碳库作用及在区域碳收支平衡中占有重要地位。选择具有典型退化特征的高寒草地为研究样地，通过野外调查、观测，样品采集和室内分析，旨在揭示不同退化演替阶段高寒草地土壤碳对植物功能群时空变异的响应机制。结论如下：.1.随退化程度加剧，植物功能群中莎草科、禾本科重要值减小，杂类草重要值增大，植物功能群由莎草科、禾本科向豆科、杂类草演替；莎草科、禾本科功能群对土壤资源的利用能力弱于杂类草和豆科功能群。.2.随退化程度加剧，功能群植物空间异质性增大，空间分布趋向复杂且非均质性变大，破坏草地植物群落结构，影响土壤有机碳空间分布，总体上不利于高寒草地生态系统的稳定。.3.随退化程度加剧，高寒草地植物地上部、地下部碳，地表枯落物碳含量空间异质性增大，引起因素以群落内的结构性因素为主，空间分布变复杂且非均质性变大，加剧了土壤有机碳等的空间异质性。.4.随退化程度加剧，退化高寒草地土壤总碳、有机碳、轻组有机碳、重组有机碳、微生物量碳、易氧化有机碳、水溶性有机碳含量和土壤过氧化氢酶、脲酶、蔗糖酶活性以及土壤二氧化碳释放速率均下降。.5.随退化程度加剧，高寒草地植物功能群与土壤碳各指标间的相关程度降低；影响土壤碳变化的因素不仅是植物功能群的演替，还受到其他因素诸如气候、土壤性质等的影响。.6.不同退化演替阶段高寒草地土壤有机碳库状态及稳定性不同，活性有机碳是土壤碳库变化的早期预警指标，随着高寒草地退化程度的加剧，土壤有机碳库的稳定性降低。.7.退化高寒草地植物功能群与土壤因子间存在相关关系，不同土壤因子与植物功能群的相关程度不同。植物功能群的分布对土壤全氮、土壤含水量等因子的变化更敏感且受到土壤含水量、全氮等的极显著影响，莎草科与土壤全氮、土壤含水量等，禾本科与土壤含水量、有机碳等具有较高的相关度，而豆科、杂类草受容重、土壤含水量等的影响更大。