FACTORS CONTROLLING ATMOSPHERIC METHANE CONSUMPTION BY TEMPERATE FOREST SOILS

Over the past 6 years (1988-1993), we have examined the effects of soil temperature, soil moisture, site fertility, and nitrogen fertilization on the consumption of atmospheric CH4 by temperate forest soils located at the Harvard Forest in Petersham, Massachusetts. We found that soil temperature is an important controller of CH4 consumption at temperatures between -5 degrees and 10 degrees C but had no effect on CH4 consumption at temperatures between 10 degrees and 20 degrees C. Soil moisture exerts strong control on CH4 consumption over a range of 60 to 100% water-filled pore space (% WFPS). As moisture increased from 60 to 100% WFPS, CH4 consumption decreased from 0.1 to 0 mg CH4-C m(-2) h(-1) because of gas transport limitations. At 20 to 60% WFPS, site fertility was a strong controller of CH4 consumption. High-fertility-sites had 2 to 3 times greater CH4 consumption rates than low-fertility sites. Nitrogen-fertilized soils (50 and 150 kg NH4NO3-N ha(-1) yr(-1)) had annually averaged CH4 consumption rates that were 15 to 64% lower than annually averaged CH4 consumption by control soils. The decrease in CH4 consumption was related to both the years of application and quantity of nitrogen fertilizer added to these soils.