Schwarz, M.T.; Oelmann, Y. & Wilcke, W. (2011): <b>Stable N isotope composition of nitrate reflects N transformations during the passage of water through a montane rain forest in Ecuador</b>. <i>Biogeochemístry</i> <b>102</b>, 195-208.
Resource Description
Title:
Stable N isotope composition of nitrate reflects N transformations during the passage of water through a montane rain forest in Ecuador
email:
wolfgang.wilcke <at> kit.edu
Karlsruhe Institute of Technology
Institute of Geography and Geoecology
Reinhard-Baumeister-Platz 1
76131 Karlsruhe
Baden-Württemberg
Germany
Abstract:
Knowledge of the fate of deposited N in the possibly N-limited, highly biodiverse north Andean forests is important because of the possible effects of N inputs on plant performance and species composition. We analyzed concentrations and fluxes<br/>
of NO3?N, NH4?N and dissolved organic N (DON) in rainfall, throughfall, litter leachate, mineral soil solutions (0.15?0.30 m depths) and stream water in a montane forest in Ecuador during four consecutive quarters and used the natural 15N abundance in NO3 during the passage of rain water through the<br/>
ecosystem and bulk d15N values in soil to detect N transformations. Depletion of 15N in NO3 and increased NO3<br/>
fluxes during the passage through the canopy and the organic layer indicated nitrification in these compartments. During leaching from the organic layer to mineral soil and stream, NO3<br/>
concentrations progressively decreased and were enriched in 15N but did not reach the d15N values of solid phase organic matter (d15N = 5.6?6.7%). This suggested a combination of nitrification and denitrification in mineral soil. In the wettest quarter, the d15N value of NO3 in litter leachate was smaller<br/>
(d15N = -1.58%) than in the other quarters (d15N = -9.38 ± SE 0.46%) probably because of reduced mineralization and associated fractionation against 15N. Nitrogen isotope fractionation of NO3 between litter leachate and stream water was smaller in the wettest period than in the other periods<br/>
probably because of a higher rate of denitrification and continuous dilution by isotopically lighter NO3-N from throughfall and nitrification in the organic layer during the wettest period. The stable N isotope composition of NO3<br/>
gave valuable indications of N transformations during the passage of water through the forest ecosystem from rainfall to the stream.
