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 ro le in ecosystem nutrient fluxes and plant nutrition. We assessed the f orms, 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 d etermined monthly from May to October, 1994 in the forest floor (Oi, O e and Oa) and the surface mineral (E) horizons. In the field studies, soluble organic N was the dominant form in the forest floor and surfac e 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 tot al soluble P. There was a clear pattern that the concentrations of sol uble 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 relate d to that in the overlying forest floor horizons. In addition to verti cal variations, water-soluble N and P concentration showed temporal va riations. In a laboratory study, the concentration of soluble organic N and P in the incubated soils decreased continuously over time, indic ating organics were depleted by microbial activity. In the field, the temporal fluxes of soluble N and P (especially P) appeared to correspo nd to litterfall inputs. (C) 1998 Elsevier Science B.V.