SOIL NITROGEN MINERALIZATION UNDER NORTHERN HARDWOOD FORESTS ALONG A SULFATE AND NITRATE DEPOSITION GRADIENT IN THE GREAT LAKES REGION

摘要

Net N mineralization (ammonification and nitrification) in the 0-10 cm mineral soil zone of five northern hardwood forest sites along a gradient of SO_4~(2-) and NO_3~- deposition from northeastern Minnesota to central lower Michigan was measured by an in situ buried bag technique at monthly intervals from September 1987 to April 1990. Soil nitrification rates (36.9 to 46.7 kg N centre dot ha~(-1) centre dot yr~(-1)) increased from north to south among the five study sites and were strongly associated with soil temperature (r= 0.87, p < 0.001). The rates of soil ammonification (66.8 to 84.1 kg N centre dot ha~(-1) centre dot yr~(-1)) and amounts of total N mineralized (103.7 to 130.6 kg N centre dot ha~(-1) centre dot yr~(-1)) did not show a clear regional trend across the gradient sites. Significant correlations between SO_4~(2-)(r= 0.82, p< 0.001), NO_3~-(r= 0.77, p= 0.003) deposition and the adjusted means of ammonium-N after removing the effects of soil temperature indicated that SO_4~(3-) andNO_3~- deposition had significantly impacts on ammonification process. Soil pH did not correspond to the gradient of H~+deposition, which was not correlated with either ammonification or nitrification rates across the study sites.