B. Michalzik et E. Matzner, Dynamics of dissolved organic nitrogen and carbon in a Central European Norway spruce ecosystem, EUR J SO SC, 50(4), 1999, pp. 579-590
Dissolved organic nitrogen and carbon (DOC) are significant in the C and N
cycle in terrestrial ecosystems. Little is known about their dynamics in th
e field and the factors regulating their concentrations and fluxes. We foll
owed the fluxes and concentrations of the two in a Norway spruce (Picea abi
es (L.) Karst.) forest ecosystem in Germany from 1995 to 1997 by sampling a
t fortnightly intervals. Bulk precipitation, throughfall, forest floor perc
olates from different horizons and soil solutions from different depths wer
e analysed for major ions, dissolved organic N and DOC. The largest fluxes
and concentrations were observed in percolates of the Oi layer, which conta
in amino N and amino sugar N as the major components. The average ratio of
dissolved organic C to N in forest floor percolates corresponded to the C/N
ratio of the solid phase. Concentrations and fluxes were highly dynamic wi
th time and decreased with depth. The largest fluxes in forest floor percol
ates occurred when the snow melted. The concentrations and fluxes of dissol
ved organic N were significantly correlated with DOC, but the correlation w
as weak, indicating different mechanisms of release and consumption. The dy
namics of dissolved organic N and DOC in forest floor percolates were not e
xplained by pH and ionic strength of the soil solution nor by the water flu
x, despite large variations in these. Furthermore, the release of these fra
ctions from the forest floor was not related to the quality and amount of t
hroughfall. Concentrations of dissolved organic N in forest floor percolate
s increased with soil temperature, while temperature effects on DOC were le
ss pronounced, but their fluxes from the forest floor were not correlated w
ith temperature. In the growing season concentrations of both dissolved org
anic N and C in forest floor percolates decreased with increasing intensity
of throughfall. Thus, the average throughfall intensity was more important
than the amount of percolate in regulating their concentrations in forest
floor percolates. Our data emphasize the role of dissolved organic N and DO
C in the N and C cycle of forest ecosystems.