Increased Rates of Soil Respiration and Microbial Enzyme Activity Under Two Complementary Experimental Warming Methods: Implications for Carbon-Climate Feedbacks

Soils contain large amounts of carbon which is susceptible to increased decomposition with increasing global surface temperatures under climate change. It is uncertain how soil carbon will react to long-term climate change because of the differences in the decomposability of carbon sources in the soils. The interaction with the above-ground plant community, which has the potential to increase carbon sequestration in biomass, is also uncertain. By observing large soil mesocosms (29000 cm3) with tulip poplar seedlings that we reciprocally transplanted along a 700 m elevation, temperature, and moisture gradient in the Appalachian Mountains, we aimed to better understand the interactions under natural field conditions. Cylindrical soil microcosms (10 x 15 cm) were also collected from elevational and latitudinal gradients and warmed in the laboratory at ambient field temperature, ambient +3 °C, and ambient +6 °C. Soil respiration increased with increasing temperature for both experiments. Microbial enzyme activity was also increased for microcosms that originated from a low native temperature site. High elevation mesocosms transplanted to low elevations also increased their microbial enzyme activity rates such that they exceeded all other treatments. This indicates that soils from high elevations and low native temperatures may be more sensitive to warming.