Beschreibung:
<jats:title>Abstract</jats:title><jats:p>The natural <jats:sup>15</jats:sup>N abundance (<jats:italic>δ</jats:italic><jats:sup>15</jats:sup>N) of epiphytes and its N sources were studied in the canopy of a lowland rainforest in Costa Rica. Vascular and non‐vascular epiphytes and canopy soils were collected from four canopy zones and analysed for N contents and <jats:italic>δ</jats:italic><jats:sup>15</jats:sup>N signals. In addition, the N concentrations and <jats:italic>δ</jats:italic><jats:sup>15</jats:sup>N signatures of bulk precipitation, throughfall and stemflow were measured during the wet and the dry season. The <jats:italic>δ</jats:italic><jats:sup>15</jats:sup>N values of epiphyte leaves decreased significantly from the lower zones (means of −3·9 and −4·3‰) to the upper zones (means of −5·4 and −6·1‰) of the canopy. In contrast, <jats:italic>δ</jats:italic><jats:sup>15</jats:sup>N signatures of canopy soils (average −0·3‰) differed little between the zones. Bulk deposition was enriched in <jats:sup>15</jats:sup>N (+4·3‰) compared to all other potential N sources and was higher than throughfall and stemflow (+0·5 to −1·3‰). <jats:italic>δ</jats:italic><jats:sup>15</jats:sup>N values of atmospheric deposition were inversely related to those of the epiphyte leaves, whereas N isotopic composition of canopy soils did not vary significantly. Consequently, it is concluded that the variations in foliar N isotope composition of epiphytes were not simply caused by utilization of isotopically different N sources, but by different <jats:sup>15</jats:sup>N discrimination during N acquisition.</jats:p>