Soil warming and trace gas fluxes: experimental design and preliminary flux results.

We conducted several experiments to determine a procedure for uniformly warming soil 5° C above ambient using a buried heating cable. These experiments produced a successful design that could: 1) maintain a temperature difference of 5° C over a wide range of environmental conditions; 2) reduce inter-cable temperture variability to ca. 1.5° C; 3) maintain a temperature difference of 5° C near the edges of the plot; and 4) respond rapidly to changes in the environment. In addition, this design required electrical power only 42% of the time. Preliminary measurements indicate that heating increased CO2 emission by a factor of ca. 1.6 and decreased the C concentration in the O soil horizon by as much as 36%. In addition, warming the soil accelerated the emergence and early growth of the wild lily of the valley (Maianthemum canadense Desf.). The relationship between CO2 flux and soil temperature derived from our soil warming experiment was consistent with data from other hardwood forests around the world. Since the other hardwood forests were warmed naturally, it appears that for soil respiration, warming the soil with buried heating cables differs little from natural, aboveground warming. By warming soil beyond the range of natural variability, a multi-site, long-term soil warming experiment may be valuable in helping us understand how ecosystems will respond to global warming.