高寒森林溪流可溶性有机碳输入/输出动态特征

Alpine forest streams are the water sources of many downstream river basins. The output of dissolved organic carbon (DOC) with stream flow is not only the source of material and energy for the downstream aquatic ecosystems, but also an important type of carbon flux in alpine forests. However, few studies have focused on the input and output dynamics of DOC in alpine forest streams. Based on the hypothesis that stream DOC input and output can be significantly mediated by the dynamics of plant litter, snowpack, and soil freeze-thaw cycle during different critical periods, a field experiment will be conducted in the alpine forest streams of the upper reaches of the Yangtze River. Methods such as field survey and continuous monitoring will be used to investigate the individual and combined effects of plant litter composition and quality changes, seasonal changes in rainfall and snowfall, and soil percolating water and freeze-thaw cycles on the input and output dynamics of stream DOC and their relationships with influencing factors such as stream and soil physicochemical properties, forest community structure, and watershed area etc. during different critical periods. Meanwhile, based on our previous research results and combined with published data on alpine forest carbon storage and fluxes, we will analyze the contribution of stream DOC input and output to the fluxes of alpine forest carbon, aiming to reveal the processes of material turnover and output in forest ecosystems. The results of this project will be useful for better understanding the role of streams as a link between montane forests and their connected aquatic ecosystems.

高寒森林溪流是众多江河流域的水源源头，其可溶性有机碳(DOC)随水体的输出不仅是下游水域生态系统重要的物质和能量来源，而且是碳迁移的重要形式，但缺乏必要的关注。基于“高寒森林溪流DOC输入/输出受不同关键时期植物残体、雪被和冻融循环等因子的综合调控”这一科学假设，拟以长江上游海拔3600m左右的高寒森林溪流为研究对象，采用野外调查和实时监测等方法研究不同关键时期植物残体组分和质量变化、季节性降雨/降雪动态、土壤渗透水与冻融循环以及三者的综合作用对溪流DOC输入/输出的影响，分析DOC输入/输出与土壤理化性质、森林群落结构、集水区面积等的相互关系。同时，基于团队前期研究结果，结合已有高寒森林碳储量和碳迁移数据，深入讨论溪流DOC输入/输出对森林碳迁移的贡献，进一步了解以DOC为代表的森林物质周转和输出过程。研究结果可为深入认识森林溪流在联系山地森林与对接水体之间的纽带作用提供一定的科学依据。

按照《项目计划书》的要求，依托前期工作基础，在2019年到2021年期间，以长江上游3600 m左右的高寒森林溪流为研究对象，采用野外调查和实时监测等方法，探讨了溪流DOC输入/输出特征及植物残体的贡献。获得一下主要研究结果：(1) 研究期间输入溪流的植物残体平均总输入量为0.52 kg/m2，输入高峰期出现在6月，溪流植物残体储量平均为1.2 kg/m2，其中木质残体储量平均为0.7 kg/m2，而非木质残体为0.5 kg/m2。不同溪流间植物残体木质与非木质残体储量及分配格局存在显著差异；(2) 集水区内，单位集水区面积DOC的最大年输出速率为13.0 t/km2。研究区溪流水体中不同形态碳的输出速率存在显著差异，表现为全碳、无机碳和有机碳的单位集水区面积输出速率分别为2.0、1.2和0.8 t/km2,表明高寒森林生态系统溶解碳可通过溪流水体输出大量流失、其中无机碳和有机碳的输出量分别占到总溶解碳的约60%和40%；(3) 不同关键时期之间，溪流DOC输出随水体流量的增加而增加，且DOC含量及输出特征与溪流长度密切相关，整体表现为长度大于30 m的溪流DOC浓度在源头大于尽头，而在长度小于30 m的溪流中表现出相反的规律。这些研究结果表明高寒森林溪流不仅是重要的碳储量库，同时也是森林碳输出的重要渠道。基于这些研究结果，在Global Change Biology，Global Ecology and Biogeography，Ecosystems，Oikos和《植物生态学报》等国内外主流期刊发表论文25篇，出版专著1部，培养博士2名，硕士2名，形成了一直从事森林生态的年轻有活力的研究团队。

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