CH4 UPTAKE AND N AVAILABILITY IN FOREST SOILS ALONG AN URBAN TO RURALGRADIENT

Concern about increases in atmospheric CH4 concentrations has resulted in investigations of the magnitude of and the factors that control ae robic soils as a sink for CH4. N additions decrease CHI consumption in temperate forest, prairie and agricultural soils, suggesting that low rates of CH4 consumption are associated with high concentrations of a vailable N. We have observed the opposite pattern in a series of oak-d ominated forest sites of similar age on similar soils located along an urban to rural land-use gradient. Low rates of CH4 consumption were o bserved in urban forest sites with low amounts of available N relative to rural sites that had high concentrations of available N. In situ c onsumption rates ranged from 6.9 to 2.1 mg CH4 m(-2) d(-1). Mean rates of consumption were 30% lower in urban than in rural and suburban for est sites, suggesting that factors associated with urbanization may de crease rates of CH4 consumption in temperate forest soils. We hypothes ize that low consumption rates of CH4 in urban forest sites are a prod uct of low rates of organic matter degradation and nutrient cycling ca used by air pollution (especially ozone) damage to forest tree leaves. Reduced rates of decomposition may result in lower rates of C and N f low from litter to soil microbial populations responsible for consumpt ion of CH4.