The Effect of Soil Warming On Organic Matter Decomposition in Highly-Weathered Soils.

Warming trends associated with climate change have the potential to increase the flux of carbon from soils, thus affecting the carbon storage capacity of the terrestrial biosphere. Previous soil warming studies have mostly been conducted on nutrient rich soils with relatively abundant organic matter, and not on low-organic matter and highly-weathered Ultisol and Oxisol soils that typify much of the lower-latitude zones of the world (ie; southeastern U.S. Piedmont, subtropics and tropics). The goal of this experiment was to determine the effect soil warming has on belowground carbon dynamics in a southeastern U.S. Piedmont forest. Warming manipulations were conducted in two habitats: closed forest canopies and canopy gaps (minimal aboveground leaf litter inputs). We measured in situ soil respiration for three years and extracellular enzyme activities during the third year of warming. Soil warming produced no effect on carbon dioxide efflux in both forest and gap habitat. Overall, extracellular enzyme activities involved in soil organic matter degradation either decreased or did not change with warming. Contrary to the results of previous warming studies, our results suggest that warming does not increase carbon dioxide efflux. Ongoing experiments are examining what mechanisms might be responsible for the lack of response, including moisture, temperature and substrate constraints on microbial activity and enzyme kinetics. Collectively these efforts will shed light on the lack of temperature response in these highly-weathered soils of the Southeast U.S.