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Wilcke, W.; Leimer, S.; Peters, T.; Emck, P.; Rollenbeck, R.; Trachte, K.; Valarezo, C. & Bendix, J. (2013): The nitrogen cycle of tropical montane forest in Ecuador turns inorganic under environmental change. Global Biogeochemical Cycles 27(4), 1194-1204.
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DOI: 10.1002/2012GB004471
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Abstract:
Abstract:
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 significantly decreased in rainfall, throughfall, and soil
solutions. This inorganic turn of the N cycle was most pronounced in rainfall and became
weaker along the flow path of water through the system until it disappeared in stream water.
Decreasing organic contributions to N cycling were caused not only 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 NO3-N concentrations and NO3-N/NH4-N
concentration ratios in throughfall and litter leachate below the thick organic layers indicated
increasing nitrification. In mineral soil solutions, in contrast, NH4-N concentrations increased and NO3-N/NH4-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.
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Keywords: |
climate change |
nitrification |
N deposition |
terrestrial N cycling |
dissolved organic N |