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

寒带和温带沼泽覆盖不到地球表面的3%，但储存了近30%的陆地碳，这些碳是数千年来土壤水分饱和积累的。天然养殖沼泽的特点是以泥炭藓为主的植被覆盖，但人类几个世纪以来一直利用泥炭提取。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，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修复的主要目标。然而，由于固碳与水平衡的密切耦合，植被组成的细微变化会对生态系统碳汇强度产生重大影响。近几十年来，恢复沼泽的物种组成发生了变化，从以苔藓植物为主的苔藓植物群落到多层乔木和禾本科植被。目前的调查报告显示，土壤碳汇强度对土壤穿透、蒸散发、总初级生产力、呼吸、净二氧化碳平衡（NEE）和土壤碳汇强度的影响相互矛盾。关于气候变化所改变的生态系统功能的最后结论尚不清楚，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草类植物是一种常见的自然保护做法，目的是减少ET和限制进一步的侵蚀，但在重建接近自然的水文条件及其对碳平衡的影响方面的有效性尚未得到最终澄清。本项目旨在对大西洋温带维管植物入侵过程中恢复后的沼泽的ET、NEE和土壤碳汇强度进行机理分析。重点将放在通过涡旋相关和室内原位测量将生态系统总ET和NEE通量划分为苔藓植物、禾本科植物和树木的贡献。研究结果用于参数化能够模拟泥炭土苔藓植物层和维管植物层的现代土壤-植被-大气-运输模型。该模型结合经验数据，量化了植物功能群通量贡献随环境条件变化的季节变化。整体过程的理解对于在变化的气候条件和植被组成下恢复的沼泽生态系统的NEE估算及其对气候变化的影响具有重要意义。对整个欧洲的恢复活动以及自然保护和减少排放措施的评估，将直接促进对植物功能群与沼泽生态系统质量和能量通量的不同相互作用的进一步了解。

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.