Partitioning of 15N-labeled ammonium and nitrate among soil, litter, below- and above-ground biomass of trees and understory in a 15-year-old Picea abies plantation

摘要: The partitioning of nitrogen deposition among soil, litter, below- and above-ground biomass trees understory vegetation was investigated in a 15-year-old Picea abies (L.) Karst. plantation the Fichtelgebirge, Germany, by labeling with 62 mg of15N tracer per square meter March 1991. Ammonium nitrate depositions were simulated on five plots each, either15N-NH4 + or15N-NO3 −, the15N pulse followed during two successive growing seasons (1991 1992). Total recovery rates entire stand ranged between 93 102% for both forms 1991, 82% June 1992. δ5 N ratios increased rapidly all compartments ecosystem. Roots soils (to 65 cm depth) showed significant15N enrichments both15N-treatments compared to reference plots. Newly grown spruce tissues more enriched than older ones, but most δ15N values found vegetation. Although much larger pool (1860 g biomass/m2) (Vaccinium myrtillus 333 g/m2, Calluna vulgaris 142 Deschampsia flexuosa 22 g/m2), ericaceous shrubs perennial grass greater sink label. Eight months after labeling, 9% ammonium 15% label understory. P.abies retained only 3% the15N-ammonium 7% the15N-nitrate. main both15N tracers where 87% 79% found. organic soil horizon (5-0 contained 63% 46% -nitrate suggesting strong immobilization microorganisms forms. application, about 16% both15N-tracers below 25 depth. This corresponds well 20% decrease 15 indicates total loss out Highly fruit bodies fungi lots (no15N addition), although did not show ratios. No transfer of15N-tracer or apparent yet.