The impacts of excessive nitrogen additions on enzyme activities and nutrient leaching in two contrasting forest soils

Nitrogen (N) deposition has increased dramatically worldwide, which may affect forest soils in various ways. In this study, we conducted a short-term manipulation experiment of N addition on two types of forest soils (urban and rural soils) found in Korea. N addition significantly decreased phenol oxidase activities in urban soil samples; however, it did not affect those in rural soils. Furthermore, N addition did not change β-glucosidase and N-acetylglucosaminidase activities, except for β-glucosidase activities in the O layer of rural soils. Changes in microbial biomass and general activity (dehydrogenase activity) were not induced by N addition, except for dehydrogenase in the A layer of urban soils. Although N addition did not change the extractable soil nutrients, organic matter, and water contents significantly, it enhanced nutrient leaching and resulted in lower pH leachate. These results suggest that excessive N addition to forest soils may induce nutrient leaching in the long-term. Overall results of our study also suggest that N addition may induce retardation of organic matter decomposition in soils; however, such a response may depend on the intensity of previous exposure to N deposition.