Impact assessment of vascular plant encroachment on water and carbon cycling in a Sphagnum dominated bog - VESBO

北方和温带的沼泽覆盖了不到3%的地球表面，但储存了近30%的陆地碳，这些碳是通过永久的土壤水分饱和而在几千年里积累起来的。天然隆起的沼泽以泥炭苔藓为主的植被覆盖为特征，但几个世纪以来，人类通过提取泥炭来使用。人工排水对生态系统功能和生物多样性的影响是多方面的，而且不仅限于二氧化碳排放量的大幅增加。重建准自然水文条件和生态系统典型植被是几十年来生态恢复的主要目标。然而，由于固碳与水分平衡的紧密耦合，植被组成的细微变化会对生态系统的碳汇强度产生重大影响。在过去的几十年里，恢复的沼泽物种组成发生了变化，从以泥炭苔藓为主的群落转变为多层乔木和禾本科植被。目前的研究报告对穿透雨、蒸散(ET)、总初级生产力、呼吸、净二氧化碳平衡(NEE)以及土壤碳汇强度的影响相互矛盾。关于气候变化引起的生态系统功能变化的最后结论尚不存在，但由于越来越多的泥炭矿区得到恢复，这一结论越来越重要。从沼泽中移除树木和禾本科植物是一种常见的自然保护措施，目的是减少ET和限制进一步的侵蚀，但对于重建接近自然的水文条件及其对碳平衡的影响的有效性尚未明确。本项目提案旨在对恢复的大西洋温带隆起沼泽在维管植物入侵过程中ET、NEE和土壤碳汇强度的机理进行分析。重点将放在通过涡旋协方差和室内现场测量将总生态系统ET和NEE通量分配到苔藓植物、禾本科植物和树木贡献上。结果被用来对现代土壤-植被-大气-运输模型进行参数化，该模型能够模拟泥炭土壤上的苔藓和维管植物层。该模型与经验数据相结合，用于量化植物功能基团通量贡献的季节变化，取决于环境条件的变化。整体过程的理解对于估算气候条件和植被组成变化下恢复的沼泽生态系统的需要具有很高的相关性，从而对它们对气候变化的影响具有重要意义。通过对整个欧洲的恢复活动以及自然保护和减排措施的评估，将直接评估植物功能组与沼泽生态系统的质量和能量通量之间的不同相互作用。

Boreal and temperate bogs cover less than 3% of the earth's surface but store nearly 30% of the terrestrial carbon, accumulated over millennia by permanent soil water saturation. Natural raised bogs are characterized by a Sphagnum-moss dominated vegetation cover, but used by humans for centuries by peat extraction. The impacts of artificial drainage on ecosystem functioning and biodiversity are numerous and not limited to the tremendously increased CO2 emissions. The re-establishment of quasi-natural hydrological conditions as well as of ecosystem-typical vegetation is the main goal of ecological restoration conducted since decades. However, due to the close coupling of carbon fixation to the water balance, subtle changes in the vegetation composition can have major impacts on the ecosystem carbon sink strength.In the last decades, a change in species composition of restored bogs from Sphagnum-dominated bryophyte communities to multi-layered tree and graminoid vegetation was observed. Current investigations report contradictory effects for the impact on throughfall, evapotranspiration (ET), gross primary productivity, respiration, net CO2 balance (NEE) as well as soil carbon sink strength. A final conclusion with respect to altered ecosystem functioning in the light of climate change is missing but of increasing importance, since more and more peat mining areas are restored. The removal of trees and graminoids from bogs is a common nature conservation practice in order to reduce ET and limit further encroachment, but the effectiveness with regard to the re-establishment of near-natural hydrological conditions and their influence on the carbon balance has not been conclusively clarified.The present project proposal aims at the mechanistic analysis of ET, NEE and soil carbon sink strength of a restored, Atlantic-temperate raised bog during vascular plant encroachment. Focus will be placed on the partitioning of total ecosystem ET and NEE fluxes by Eddy Covariance and chamber measurements in situ into bryophyte, graminoid and tree contributions. Results are used to parameterize a modern soil-vegetation-atmosphere-transport model able to simulate bryophyte and vascular plant layers on peat soil. The model, jointly with the empirical data, is used to quantify seasonal changes in plant functional group flux contributions depending on altered environmental conditions. The holistic process understanding is of high relevance for the NEE estimation of restored bog ecosystems under changing climatic conditions and vegetation compositions and thus, their impact on climate change. The improved knowledge about different interactions of plant functional groups with mass and energy fluxes of the bog ecosystem will be directly valorised by the assessment of restoration activities as well as nature conservation and emission mitigation measures throughout Europe.