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Media type:
E-Article
Title:
Stable N isotope composition of nitrate reflects N transformations during the passage of water through a montane rain forest in Ecuador
Contributor:
Schwarz, Martin Thilo;
Oelmann, Yvonne;
Wilcke, Wolfgang
Published:
Springer, 2011
Published in:
Biogeochemistry, 102 (2011) 1/3, Seite 195-208
Language:
English
ISSN:
0168-2563;
1573-515X
Origination:
Footnote:
Description:
<p>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 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 ecosystem and bulk δ¹⁵N values in soil to detect N transformations. Depletion of ¹⁵N in NO₃ ⁻ and increased NO₃ ⁻-N 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⁻ concentrations progressively decreased and were enriched in ¹⁵N but did not reach the δ¹⁵N values of solid phase organic matter (δ¹⁵N = 5.6-6.7%₀). This suggested a combination of nitrification and denitrification in mineral soil. In the wettest quarter, the δ¹⁵N value of NO ₃ ⁻ in litter leachate was smaller (δ¹⁵N = -1.58%₀) than in the other quarters (δ¹⁵N = -9.38 ± SE 0.46%₀) 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 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 ⁻ gave valuable indications of N transformations during the passage of water through the forest ecosystem from rainfall to the stream.</p>