Fluxes of dissolved organic and inorganic nitrogen in relation to stand characteristics and latitude in Scots pine and Norway spruce stands in Finland

We monitored the fluxes of nitrogen (N) compounds in throughfall (TF) and in percolation water (PW) in Scots pine and Norway spruce stands in Finland, and explored their dependence on N bulk deposition (BD) rates and general site and stand characteristics. During 1998-2004, N fluxes in BD, TF, and PW were low and remained relatively constant. Inorganic N was retained in the ecosystem (BD > TF > PW) more effectively in spruce stands, while the fluxes of dissolved organic nitrogen (DON) correspondingly increased. The canopy retention of inorganic N was correlated with the net increase in TF DON. BD DON was relatively constant, while the TF DON and BD deposition of inorganic N increased towards the south. DON accounted for 14% of the BD N, 48% of N in TF in spruce and 31% in pine stands, and 80% of the total N in PW. Stand characteristics (e.g. stand age) affected the TF fluxes of both inorganic N and DON, while only the NH4-N flux in PW was related to deposition rates.