Fluxes of water-soluble nitrogen and phosphorus in the forest floor and surface mineral soil of a boreal aspen stand

Water-soluble nitrogen (N) and phosphorus (P) may play an important role in ecosystem nutrient fluxes and plant nutrition. We assessed the forms, concentrations and distribution patterns of water-soluble N and P in a soil under aspen stands in the southern boreal forest of Canada, Soluble organic N, NH4+-N, NO3--N, organic P, and inorganic P were determined monthly from May to October, 1994 in the forest floor (Oi, Oe and Oa) and the surface mineral (E) horizons. In the field studies, soluble organic N was the dominant form in the forest floor and surface mineral horizons. On average, soluble organic N accounted for 85% of the total soluble N, followed by NH4+-N (13%) and NO3--N (2%). Unlike N, inorganic P was the dominant form and accounted for 75% of the total soluble P. There was a clear pattern that the concentrations of soluble organic N and P decreased in the order of Oi > Oe > Oa >> E. The concentrations of soluble organic N and P in the E horizon were related to that in the overlying forest floor horizons. In addition to vertical variations, water-soluble N and P concentration showed temporal variations. In a laboratory study, the concentration of soluble organic N and P in the incubated soils decreased continuously over time, indicating organics were depleted by microbial activity. In the field, the temporal fluxes of soluble N and P (especially P) appeared to correspond to litterfall inputs. (C) 1998 Elsevier Science B.V.