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>
Resource Description
Title:
Response of nutrient cycles of an old-growth montane forest in Ecuador to experimental low-level nutrient amendments
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:
THESIS
Degree:
phd
Degree Institution:
Johannes Gutenberg University Mainz
Total Pages:
142
Metadata Provider:
Individual:
Wolfgang Wilcke
Contact:
email:
wolfgang.wilcke <at> kit.edu
Karlsruhe Institute of Technology
Institute of Geography and Geoecology
Reinhard-Baumeister-Platz 1
76131 Karlsruhe
Baden-Württemberg
Germany
