Abstract booklet - gtö – Society for Tropical Ecology

238 SCIENTIFIC POSTER SESSION | FOYERSCIENTIFIC POSTER SESSION | FOYER239Free contributionDO CURRENT POPULATION STRUCTURES REALLY PREDICTCOMMUNITY DYNAMICS OF VASCULAR EPIPHYTES?Katrin Wagner 1 , Glenda Mendieta-Leiva 1 , Gerhard Zotz 11Universität Oldenburg, Oldenburg, DE, nirtak.wagner@gmx.deTopic: The Andean biodiversity hotspot and its future: biodiversity, eco-systemfunctioning and ecosystem services under environmental changeTHE IMPORTANCE OF NITROGEN FOR TREE SEEDLING NUTRITIONALONG AN ELEVATIONAL TRANSECT OF ANDEAN FORESTS IN SOUTHECUADORBärbel Wittich 1 , Juergen Homeier 1 , Dietrich Hertel 1 , Christoph Leuschner 11Universität Göttingen, Göttingen, DE, baerbelw@gmx.netWEDNESDAY | FOYERThere is a long-standing debate whether current population structure of plantsmay be used to predict future change in population size. This notion, which wasimplicitly and explicitly prevalent for decades, has been empirically rejected fortrees in a number of recent papers. However, a close correlation of populationstructure and species abundance that was found in a census of vascularepiphytes in Panama, led us to suggest that size distributions of populations canbe still used to predict changes in the case of vascular epiphyte communities.Arguably, there are differences between tree and epiphyte communities due tofundamental differences in the ecology of these life-forms.Here, we provide a direct test of this notion. We take advantage of two extensivedata sets. These data sets comprise together about 20,000 individuals out of ca.120 species in two lowland forests of Panama, which have been censused twiceover a period of eight and nine years, respectively. In each epiphyte communitywe compare the population structure with changes in species abundance intime, excluding rare species, filmy ferns and hemiepiphytes.Tree growth in many tropical lowland forests is primarily limited by P while plantavailableN seems to be relatively abundant. Tropical montane forests, in contrast,most often grow on younger soils where N should be short in supply whereas Plimitation of growth should be of secondary importance compared to the olderlowland soil. In tropical mountains, soils may further loose N through erosion orvia large DON exports in a humid climate.Changes in nitrogen availability may affect tree seedling performance in manydifferent ways, such as growth rate, leaf morphology and physiology. For tropicaltrees the preferred N form is barely known. We aimed at testing the hypothesisthat trees at lower montane elevation utilise both, ammonium and nitrate, thoseat upper montane elevation predominantly ammonium and also organic N. Amesocosm experiment was established with tree seedlings at three elevations(1000, 2000, and 3000 m a.s.l.). The experiment was run with representative treespecies of each elevation. The seedlings were collected in the natural forest bycarefully selecting individuals of comparable size and stature and planted inpots of 10 l volume using local topsoil material to provide close to natural soilconditions including the mycorrhizal fungi.N was applied to part of the seedlings. For 12 month several variables weremonitored, such as root collar diameter, shoot length, leaf morphology, leaflife span, and photosynthesis. With the remaining part of the seedlings a 15Ntracer study was conducted to detect differential preferences in the uptake ofammonium, nitrate, and organic N by the trees at 1000 m, 2000 m, and 3000m elevation under assumed conditions of P or N limitation. Uptake rates of therespective N form were analyzed by harvest of the seedlings at 120 hours afterapplications and separate analyses of roots, stems and leaves.Wednesday WEDNESDAY 16:00 | FOYER | FoyergtöSociety for Tropical Ecology | Gesellschaft für Tropenökologie e.V. Status and future of tropical biodiversity | Frankfurt, 21 - 24 February 2011gtö