Soil warming in a northern hardwood forest: trace gas fluxes and leaf litter decomposition

The response of trace gas fluxes (CO2 CH4 and N-2) and litter decomposition to increased soil temperature was evaluated in a northern hardwood forest. Four experimental plots (10 x 10 m) had heating cables installed within the forest floor. Temperatures at 5 cm were increased 2.5, 5.0, or 7.5 degrees C in individual heated plots during the field season in 1993 and 1994. The fourth plot was a cabled, nonheated reference. Trace gas fluxes were monitored using closed chambers. Soil moisture was monitored using tensiometers and time domain reflectometry. Changes in leaf litter decomposition were quantified using litter bags for American beech (Fagus grandifolia Ehrh.) and sugar maple (Acer saccharum Marsh.) litter. Fluxes of CO2 increased exponentially with increased soil temperatures within treatments and were higher in heated plots than in the reference plot. Temperature coefficients (Q(10)) and mass remaining of American beech leaf litter decreased with the level of heating, suggesting a nonlinear microbial response to elevated temperatures. Soil water content exhibited the most influence on CH4 and N2O flux in the second season. The experimental manipulations showed the importance of evaluating the influence of soil temperature coupled with effects of N and moisture availability.