PDF(Pubmed)
Abstract：
Methane (CH4) is a powerful greenhouse gas with ongoing efforts aiming to quantify and map emissions from natural and managed ecosystems. Wetlands play a significant role in the global CH4 budget, but uncertainties in their total emissions remain large, due to a combined lack of CH4 data and fuzzy boundaries between mapped ecosystem categories. European floodplain meadows are anthropogenic ecosystems that originated due to traditional management for hay cropping. These ecosystems are seasonally inundated by river water, and straddle the boundary between grassland and wetland ecosystems; however, an understanding of their CH4 function is lacking. Here, we established a replicated outdoor floodplain-meadow mesocosm experiment to test how water table depth (45, 30, 15 cm below the soil surface) and plant composition affect CH4 fluxes over an annual cycle. Water table was a major controller on CH4, with significantly higher fluxes (overall mean 9.3 mg m-2 d-1) from the high (15 cm) water table treatment. Fluxes from high water table mesocosms with bare soil were low (mean 0.4 mg m-2 d-1), demonstrating that vegetation drove high emissions. Larger emissions came from high water table mesocosms with aerenchymatous plant species (e.g. Alopecurus pratensis, mean 12.8 mg m-2 d-1), suggesting a role for plant-mediated transport. However, at low (45 cm) water tables A. pratensis mesocosms were net CH4 sinks, suggesting that there is plasticity in CH4 exchange if aerenchyma are present. Plant cutting to simulate a hay harvest had no effect on CH4, further supporting a role for plant-mediated transport. Upscaling our CH4 fluxes to a UK floodplain meadow using hydrological modelling showed that the meadow was a net CH4 source because oxic periods of uptake were outweighed by flooding-induced anoxic emissions. Our results show that floodplain meadows can be either small sources or sinks of CH4 over an annual cycle. Their CH4 exchange appears to respond to soil temperature, moisture status and community composition, all of which are likely to be modified by climate change, leading to uncertainty around the future net contribution of floodplain meadows to the CH4 cycle.
摘要：
甲烷（CH4）是一种强大的温室气体，正在努力量化和绘制自然和管理生态系统的排放图。湿地在全球CH4预算中发挥着重要作用，但是总排放量的不确定性仍然很大，由于缺乏CH4数据和映射的生态系统类别之间的模糊边界。欧洲洪泛区草甸是人为生态系统，起源于传统的干草种植管理。这些生态系统季节性地被河水淹没，跨越草地和湿地生态系统之间的边界；然而，缺乏对其CH4功能的理解。这里,我们建立了一个重复的室外洪泛区-草甸中观实验，以测试地下水位深度（土壤表面以下45、30、15厘米）和植物组成如何影响CH4通量。地下水位是CH4的主要控制器，高（15cm）地下水位处理的通量明显更高（总体平均9.3mgm-2d-1）。来自裸露土壤的高地下水位中观的通量较低（平均0.4mgm-2d-1），证明了植被驱动了高排放。较大的排放来自高地下水位的中观，其中有一个完整的植物物种（例如，平均12.8毫克m-2d-1)，提示植物介导的运输的作用。然而,在低（45厘米）地下水位A.pratensis介观是净CH4汇，这表明，如果存在aerenchyma，则CH4交换具有可塑性。模拟干草收获的植物切割对CH4没有影响，进一步支持了植物介导的运输作用。使用水文模型将我们的CH4通量扩大到英国洪泛区草甸，结果表明该草甸是净CH4源，因为洪水引起的缺氧排放超过了吸收的氧化期。我们的结果表明，洪泛区草地在一个年度周期中既可以是CH4的小来源，也可以是CH4的汇。它们的CH4交换似乎对土壤温度有反应，水分状况和群落组成，所有这些都可能被气候变化所改变，导致洪泛区草甸对CH4循环的未来净贡献存在不确定性。
