Cite as:
Wullaert, H. (2010): <b>Response of nutrient cycles of an old-growth montane forest in Ecuador to experimental low-level nutrient amendments</b> Johannes Gutenberg University Mainz, <i>phd thesis</i>

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Title: Response of nutrient cycles of an old-growth montane forest in Ecuador to experimental low-level nutrient amendments
Short Name: NUMEX N&P
FOR816dw ID: 885
Publication Date: 2010-07-02
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Resource Owner(s):
Individual: Hans Wullaert
Atmospheric nitrogen (N) and phosphorus (P) depositions are expected to increase in the tropics<br/> as a consequence of increasing human activities in the next decades. Furthermore, a possible<br/> shortened El Niño Southern Oscillation cycle might come along with more frequent calcium (Ca)<br/> depositions on the eastern slope of the Ecuadorian Andes originating from Saharan dust. It is<br/> crucial to understand the response of the old-growth montane forest in Ecuador to increased<br/> nutrient deposition to predict the further development of this megadiverse ecosystem.<br/> I studied experimental additions of N, P, N+P and Ca to the forest and an untreated<br/> control, all in a fourfold replicated randomized block design. These experiments were conducted<br/> in the framework of a collaborative research effort, the NUtrient Manipulation EXperiment<br/> (NUMEX). I collected litter leachate, mineral soil solution (0.15 and 0.30 m depths), throughfall<br/> and fine litterfall samples and determined N, P and Ca concentrations and fluxes. This approach<br/> also allowed me to assess whether N, P and/or Ca are limiting nutrients for forest growth.<br/> Furthermore, I evaluated the response of fine root biomass, leaf area index, leaf area and specific<br/> leaf area, tree diameter growth and basal area increment contributed from a cooperating group in<br/> the Ca applied and control treatments.<br/> During the observation period of 16 months after the first fertilizer application, less than<br/> 10, 1 and 5% of the applied N, P and Ca, respectively, leached below the organic layer which<br/> contained almost all roots but no significant leaching losses occurred to the deeper mineral soil.<br/> Deposited N, P and Ca from the atmosphere in dry and wet form were, on balance, retained in the<br/> canopy in the control treatment. Retention of N, P and Ca in the canopy in their respective<br/> treatments was reduced resulting in higher concentrations and fluxes of N, P and Ca in<br/> throughfall and litterfall. Up to 2.5% of the applied N and 2% of the applied P and Ca were<br/> recycled to the soil with throughfall. Fluxes of N, P and Ca in throughfall+litterfall were higher in<br/> the fertilized treatments than in the control; up to 20, 5 and 25% of the applied N, P and Ca,<br/> respectively, were recycled to the soil with throughfall+litterfall.<br/> In the Ca-applied plots, fine root biomass decreased significantly. Also the leaf area of the<br/> four most common tree species tended to decrease and the specific leaf area increased<br/> significantly in Graffenrieda emarginata Triana, the most common tree species in the study area.<br/> These changes are known plant responses to reduced nutrient stress. Reduced aluminium (Al)<br/> toxicity as an explanation of the Ca effect was unlikely, because of almost complete organocomplexation<br/> of Al and molar Ca:Al concentration ratios in solution above the toxicity threshold.<br/> The results suggest that N, P and Ca co-limit the forest ecosystem functioning in the<br/> northern Andean montane forests in line with recent assumptions in which different ecosystem<br/> compartments and even different phenological stages may show different nutrient limitations<br/> (Kaspari et al. 2008). I conclude that (1) the expected elevated N and P deposition will be<br/> retained in the ecosystem, at least in the short term and hence, quality of river water will not be<br/> endangered and (2) increased Ca input will reduce nutrient stress of the forest.
Literature type specific fields:
Degree: phd
Degree Institution: Johannes Gutenberg University Mainz
Total Pages: 142
Metadata Provider:
Individual: Wolfgang Wilcke
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