Organic carbon cycling in Taylor Valley, Antarctica: quantifying soil reservoirs and soil respiration

Organic carbon reservoirs and respiration rates in soils have been calculated for most major biomes on Earth revealing patterns related to temperature, precipitation, and location. Yet data from one of the Earth's coldest, driest, and most southerly soil ecosystems, that of the McMurdo Dry Valleys of Antarctica, are currently not a part of this global database. In this paper, we present the first regional calculations of the sail organic carbon reservoirs in a dry valley ecosystem (Taylor Valley) and report measurements of CO2 efflux from Antarctic soils. Our analyses indicate that, despite the absence of visible accumulations of organic matter in most of Taylor Valley's arid soils, this soil environment contained a significant percentage (up to 72%) of the seasonally unfrozen organic carbon reservoir in the terrestrial ecosystem. Field measurements of soil CO2-efflux in Taylor Valley soils were used to evaluate biotic respiration and averaged 0.10 +/- 0.08 mu mol CO2 m(-2) s(-1). Laboratory soil microcosms suggested that this respiration rate was sensitive to increases in temperature, moisture, and carbon addition. Finally, a steady-state calculation of the mean residence time for organic carbon in Taylor Valley soils was 23 years. because this value contradicts all that is currently known about carbon cycling rates in the dry valleys, we suggest that the dry valley soil carbon dynamics is not steady state. Instead, we suggest that the dynamic is complex, with at least two (short- and la,ng-term) organic carbon reservoirs. We also suggest that organic carbon in the dry valley soil environment may be more important, and play a more active role in long-term ecosystem processes, than previously believed.