Background
In the introduction to the report of their recently concluded study, the authors enunciate one of the purposes for undertaking it, writing that "if ecosystem carbon stocks increase with warming, their greater net uptake of CO2 would slow increases in concentrations of this greenhouse gas in the atmosphere, providing a negative feedback to further greenhouse warming."

What was done
Working on the easternmost island of Stepping Stones (64°47'S, 64°04'W) near Palmer Station along the west coast of the Antarctic Peninsula, Day et al. used small greenhouses to warm daytime and diel canopy air temperatures by 2.3 and 1.3°C, respectively, as well as alter the ultraviolet light regime of the local tundra, which is inhabited by two prostrate perennial vascular plants (Antarctic pearlwort and hairgrass), a variety of mosses, and an occasional lichen and liverwort. Then, after four growing seasons with this temperature treatment, plus an unwarmed control treatment, they determined the mass of all above- and below-ground organic materials and their carbon (C) and nitrogen (N) contents.

What was learned
The three researchers report that the four seasons of warming "resulted in a substantial increase (23-34%) in total C in this ecosystem," due to "greater aboveground plant biomass, as well as greater mass of the litter layer and organic soil horizon." In addition, they say the litter and organic soil pools "were likely more recalcitrant to decomposition, based on their higher C:N values."

What it means
In light of the findings of this study, it would appear that a warming of Antarctic tundra ecosystems would indeed provide "a negative feedback to further greenhouse warming," as suggested by Day et al., and that a warming-induced loss of some of the ice covering parts of the continent would likely accelerate the phenomenon.