2010-2012 Summertime (May-Aug) Ecosystem Respiration (flux, 14C data isoflux, pore space data) at N Mnt. Snowpack Manipulation

Measurements of ecosystem respiration in high arctic prostrate dwarf-shrub tundra. Measurements were conducted from mid June to the end of August in 2010, 2011 and 2012 at a long-term snowpack manipulation experiment: consisting of two 1.2 m tall snow fences erected in the summer of 2003. Fences were aligned perpendicular to the dominant winter wind direction and snow naturally accumulates on the leeward side in a continuously tapering drift. At each fence, 2.0x0.8 m2 plots were delimited within three larger, pre-established main plots at each of three levels of winter snowpack: ambient (control, ~0.25 m), intermediate (SFM, ~0.55 m), and deep (SFH, ~1.1 m). Plots were oriented to span the transition between vascular plants and bare soil/cryptogamic crust, such that each comprised approximately 50%, to facilitate scaling from the plot to ecosystem level. Measurements were taken during the snow-free period from end of May-early June for the ambient conditions, when plots became snow-free and it was possible to clearly locate the chamber base without compacting snow, to the 20th of August in 2010, 2011 and 2012. Ecosystem respiration and pore space carbon dioxide CO2 concentrations were measured two to three times per week. Ecosystem respiration was determined through the use of dark chambers (30 cm i.d., 8 L V). In June, collars were inserted to ~2 cm depth, sealed with soil material on the outside, and left in place for the sampling season. To calculate Reco, air was circulated between the chamber's headspace connected to an infrared gas analyzer and a data logger (LI-840, LI-1400, LI-COR Biosciences, Lincoln, NE, USA) at a rate of 0.5 L min-1. Flux rates were estimated from the slope of time vs. CO2 concentration curves using linear regression. In parallel, we measured soil temperature (15-077, Fisher Scientific, resolution ±0.1oC) at 5 and 10 cm depth and soil water content (SWC, Hydrosense, Campbell Scientific, Logan, UT, USA, resolution ±0.1%) at 5 cm depth.高北极地区匍匐矮灌木冻原的生态系统呼吸（ecosystem respiration）测量。本次测量于2010、2011、2012年的6月中旬至8月末开展，实验场地为一项长期积雪覆盖调控实验：该实验于2003年夏季架设两座高1.2 m的雪栅栏（snow fences），栅栏垂直于冬季主导风向布置，背风侧会自然形成逐渐变薄的积雪堆（snow drift）。 在每座栅栏处，于三个预先设置的大样地内划定2.0×0.8 m²的小样地，这三个大样地对应三种冬季积雪水平：自然对照（ambient，约0.25 m）、中等积雪（SFM，约0.55 m）与深厚积雪（SFH，约1.1 m）。小样地的朝向横跨维管植物与裸土/隐花植物结皮（cryptogamic crust）的过渡带，两类覆盖物占比各约50%，以方便从样地尺度拓展至生态系统尺度。 测量时段为无雪期，即对照样地积雪消融、可清晰放置气室底座且无需压实积雪的5月末至6月初，至2010、2011、2012年的8月20日。实验每周开展2至3次测量，内容包括生态系统呼吸与孔隙空间二氧化碳（CO₂）浓度。 生态系统呼吸采用暗室（dark chamber，内径30 cm，体积8 L）法测定：6月时将气室环（collars）插入约2 cm深度，外部用土壤密封，整个采样季保留原位不动。计算生态系统呼吸速率（Reco）时，以0.5 L·min⁻¹的速率将空气在气室顶空、红外气体分析仪与数据记录仪（LI-840、LI-1400，LI-COR Biosciences，美国内布拉斯加州林肯市）之间循环。通量速率通过时间-CO₂浓度曲线的斜率，采用线性回归（linear regression）法估算。 与此同时，在5 cm与10 cm深度处测量土壤温度（型号15-077，Fisher Scientific，分辨率±0.1 ℃），并在5 cm深度处测量土壤含水量（soil water content, SWC，型号Hydrosense，Campbell Scientific，美国犹他州洛根市，分辨率±0.1%）。