PARENT SESSION
Oral Session #44: Global Change and Climate Change.
Presiding: C. Wessman
Tuesday, August 6. 1:00 PM to 4:45 PM. Grand Ballroom West, Radisson.

Soil warming and carbon-cycle feedbacks to the climate system.

Melillo, Jerry^*,1, Steudler, Paul¹, Aber, John², Newkirk, Kathleen¹, Lux, Heidi¹, Bowles, Francis³, Catricala, Christina¹, Magill, Alison², Ahrens, Toby¹, Morrisseau, Sarah¹, ¹ The Ecosystems Center, Woods Hole, MA² Complex Systems Research Center, Durham, NH³ Research Designs, Woods Hole, MA

ABSTRACT- How much will the Earth warm over the 21^st century as greenhouse gases, most notably CO₂ from fossil fuel burning and changes in land use, accumulate in the atmosphere? Climate experts project that the Earth's mean surface temperature will increase by 1.4 to 5.8^oC by 2100. The range of projections is large because we are uncertain about a number of factors that will affect atmospheric CO₂ concentrations in the future. For instance, we do not know whether land ecosystems will take up atmospheric CO₂ and store it as organic carbon in plants and soils thereby slowing future temperature increases, or release CO₂ to the atmosphere as warming accelerates soil organic matter decay. In a decade-long soil warming experiment in a mid-latitude forest in central Massachusetts, we have measured the responses of soil carbon and nitrogen dynamics to a year-round soil temperature increase of 5^oC. We have found that while soil warming accelerates soil organic matter decay and, in the short term, CO₂ flux to the atmosphere, it also increases the availability of mineral N to plants. This increase in nitrogen availability creates conditions needed for increases in carbon storage in these ecosystems where tree growth is nitrogen limited. For many mid-latitude forests, warming may actually stimulate carbon storage at the ecosystem level and thus slow the rate of climate change.

KEY WORDS: soil warming, climate change, carbon and nitrogen cycling