| Summary: | 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.
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