Abstract booklet - gtö – Society for Tropical Ecology

106 PARALLEL SESSION HALL H IV | PLANT PHYSIOLOGYPARALLEL SESSION HALL H IV | PLANT PHYSIOLOGY 107EFFECTS OF AN EXPERIMENTAL SOIL DESICCATION ON THE ABOVE-AND BELOWGROUND BIOMASS PRODUCTION IN A PERHUMIDPRIMARY FOREST IN SULAWESI, INDONESIA.SIZE-DEPENDENT CHANGES IN LEAF PHYSIOLOGY AND NON-STRUCTURAL CARBOHYDRATE CONTENT IN TWO CARIBBEAN TREESPECIES.Gerald Moser 1 , Bernhard Schuldt 2 , Dietrich Hertel 2 , ChristophLeuschner 21Giessen University, Gießen, DE, Gerald.Moser@bio.uni-giessen.de, 2 GöttingenUniversity, Göttingen, deAdam R. Martin 1 , Sean C. Thomas 11University of Toronto, Toronto, CA, adam.martin@utoronto.caWEDNESDAY 11:45 Hall H IVIn this ecosystem experiment we studied if primary forest trees in a perhumidregion are vulnerable to ENSO droughts, which plant traits determine thedrought sensitivity, and if forest stability may be affected.To simulate an ENSO drought 3 throughfall displacement roofs and 3 controlplots (each 40mx40m) were installed in a premontane rainforest in the LoreLindu National Park, Central Sulawesi. The roofs were closed from May 2007until May 2009. During the first year of desiccation roof cover was increasedfrom 60 to 90% of the plot area.After 2 years of desiccation we observed no significant changes in fine rootbiomass or production, in tree leaf litter fall, in stem diameter increment or treemortality. During the 2nd year a significant decrease of stem wood productionoccurred, which was greatest in the predominant Fagaceae Castanopsisacuminatissima, forming the highest trees in the stand. This observed trendcould provoke a shift in the dominance structure and stability of the studiedpremontane rainforest, if pre-dictions from climate change models for moreoften and sev-ere ENSO droughts in this region hold true.In tropical trees, onset of reproduction is likely to induce changes in leafphysiological traits and non-structural carbohydrate (NSC) content in woodytissues. For example, as resources are increasingly allocated to reproductivestructures, one may expect to observe commensurate declines in photosyntheticcapacity, leaf nitrogen (N), and/or wood NSC content following reproductiveonset. While several studies have detected such patterns in temperate treespecies, currently no such comparable studies exist from tropical tree species. Inthis study, we sough to evaluate the influence of reproduction on size-dependentchanges in leaf physiology and NSC content in stem-wood and branches, for twoDominican rainforest tree species (Dacryodes excelsa (Burseraceae) and Miconiamirabilis (Melastomataceae)). Using reproductive surveys, we estimated therelative size at onset of maturity (RSOM) to be 10.4 cm DBH in M. mirabilis, and20.1 cm in D. excelsa. Preliminary results suggest that in both species leaf areaand leaf N decline following reproductive onset, while leaf C:N ratio increases.Conversely, leaf mass per area (LMA) increased monotonically with tree sizein both species. We observed subtle size-dependent declines in NSC pools instem wood and branches following reproductive onset in both species, yet atno sizes were NSC pools completely depleted in any woody tissues. Our resultsthus indicate that size-dependent changes in a suite leaf traits (i.e. leaf area,leaf N, C:N ratio) are in response to resource allocation to reproduction, whileother traits (i.e. LMA) change in response to vertical light gradients throughthe forest canopy. Additionally, declines in wood NSC content demonstratesize-dependent shifts in resource allocation from storage to reproduction.However, we suggest that because NSC pools were not completely depleted, itis ultimately unlikely that growth in tropical trees is carbon limited, even at laterontogenetic stages.WEDNESDAY 12:00 Hall H IVgtöSociety for Tropical Ecology | Gesellschaft für Tropenökologie e.V. Status and future of tropical biodiversity | Frankfurt, 21 - 24 February 2011gtö