Large Canopy Exchange Fluxes of Inorganic and Organic Nitrogen and Preferential Retention of Nitrogen by Epiphytes in a Tropical Lowland Rainforest |
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Authors: | Nina Hinko-Najera Umana Wolfgang Wanek |
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Institution: | 1. Department of Forest and Ecosystem Science, The University of Melbourne, Water Street, Creswick, Victoria, 3363, Australia 2. Department of Chemical Ecology and Ecosystem Research, University of Vienna, Vienna Ecology Centre, Althanstrasse 14, A-1090, Vienna, Austria
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Abstract: | Little is known about how tropical forest canopies interact with atmospheric nitrogen deposition and how this affects the internal nutrient dynamics and the processing of external nutrient inputs. The objectives of this study therefore were (1) to investigate gross and net canopy nitrogen (N) fluxes (retention and leaching) and (2) the effect of canopy components on net canopy N retention. Tracers were applied on detached branches in a tropical wet lowland rainforest, Costa Rica. A novel 15N pool dilution method showed that gross canopy fluxes (retention and leaching) of NO3 ?, NH4 +, and dissolved organic nitrogen (DON) were remarkably higher than net throughfall fluxes. Gross fluxes of NH4 + and NO3 ? resulted in a negligible net flux whereas DON showed net uptake by the canopy. The highest quantity of 15N was recovered in epiphytic bryophytes (16.4%) although the largest biomass fraction was made up of leaves. The study demonstrates that tracer applications allow investigation of the dynamic and complex canopy exchange processes and that epiphytic communities play a major role in solute fluxes in tree canopies and therefore in the nutrient dynamics of tropical rain forests. |
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