Wetlands have been recognized as a soil carbon (C) sink due to low decomposition. As decomposition is largely controlled by the availability of soil nitrogen (N), an elevated anthropogenic N input could influence the C balance in wetlands. However, the effects of the form of N on decomposition are poorly understood. Here, a 54-day laboratory incubation experiment was conducted, with a diel cycle (day: 22 °C for 13 h; night: 17 °C for 11 h) in order to determine how the dominant N form influences the mineralization of soil C in two adjacent wetland soils, with distinct physicochemical characteristics. Three combinations of N compounds were added at three different rates (0, 30, 60 kg N ha-1 yr-1): Ammonium dominant (NH4Cl + NH4NO3); nitrate dominant (NH4NO3 + NaNO3); and ammonium nitrate treatments (NH4NO3). In the acidic soil, the CO2 efflux was reduced with N additions, especially with NH4NO3 treatment. In addition, decreases in the microbial enzyme activities (β-glucosidase, N-acetyl-glucosaminidase, phosphatase, and phenol oxidase) and soil pH were observed with NH4NO3 and NH4+-dominant treatment. Under alkaline conditions, marginal changes in response to N additions were observed in the soil CO2 efflux, extractable DOC, simple substrate utilization, enzyme activities and pH. A regression analysis revealed that the changes in pH and enzyme activities after fertilization significantly influenced the soil CO2 efflux. Our findings suggest that the form of N additions could influence the rate of C cycling in wetland soils via biological (enzyme activities) and chemical (pH) changes.
Bibliographical noteFunding Information:
This research was supported by the Korea Student Aid Foundation (Grant No. S2-2009-000-00449-1 ). We are grateful to PGA for the field sampling, the Ecological Engineering Laboratory at Yonsei University for their warm advices and experimental support, the Ecosystem Ecology Laboratory at Korea University for discussion and use of the elemental analyzer, and Dr. Haeguen Chung, Dr. Donggil Kim, and Dr. Sharon Billings for their invaluable comments. In particular, we appreciate anonymous referees for their very constructive criticisms and comments on our early drafts of this paper. H. Kang is grateful to NRF ( 2010-0028708 ) for financial support.
All Science Journal Classification (ASJC) codes
- Soil Science