Publication Date:
2013-11-06
Description:
[1] Water-bound nitrogen (N) cycling in temperate terrestrial ecosystems of the northern hemisphere is today mainly inorganic because of anthropogenic release of reactive N to the environment. In little industrialized and remote areas, in contrast, a larger part of N cycling occurs as dissolved organic N (DON). In a north Andean tropical montane forest in Ecuador, the N cycle changed markedly during 1998–2010 along with increasing N deposition and reduced soil moisture. The DON concentrations and the fractional contribution of DON to total N (TN) significantly decreased in rainfall (RF), throughfall (TF), and soil solutions (SS). This inorganic turn of the N cycle was most pronounced in RF and became weaker along the flow path of water through the system until it disappeared in stream water (SW). Decreasing organic contributions to N cycling were not only caused by increasing inorganic N input but also by reduced DON production and/or enhanced DON decomposition. Accelerated DON decomposition might be attributable to less waterlogging and higher nutrient availability. Significantly increasing NO 3 -N concentrations and NO 3 -N/NH 4 -N concentration ratios in TF and litter leachate (LL) below the thick organic layers indicated increasing nitrification. In mineral soil solutions, in contrast NH 4 -N concentrations increased and NO 3 -N/NH 4 -N concentration ratios decreased significantly suggesting increasing net ammonification. Our results demonstrate that the remote tropical montane forests on the rim of the Amazon basin experienced a pronounced change of the N cycle in only one decade. This change likely parallels a similar change which followed industrialization in the temperate zone of the northern hemisphere more than a century ago.
Print ISSN:
0886-6236
Electronic ISSN:
1944-9224
Topics:
Biology
,
Chemistry and Pharmacology
,
Geography
,
Geosciences
,
Physics
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