Influence of Species Functional Strategy on Leaf Stoichiometric Responses to Fertilizer in a Bornean Heath Forest

The distribution of Bornean heath forest on white sand soils is believed to be due to element limitation and soil acidity. To determine the impact of both element limitation and soil acidity on tropical heath forest, we established a soil fertilization experiment to investigate the impact that increased soil N availability and reduced soil pH (using lime/CaCO3) had on a range of elements in tree leaves. We hypothesized that alterations in soil resource availability would cause changes in the tree leaf N:P ratio and concentrations of other elements and these changes would be influenced by species' functional strategies. The experiment was carried out in a Bornean heath forest on infertile soil over a 2-year period. We selected 10 common tree species, spanning acquisitive to conservative strategies and tested whether tree species functional strategies influenced tree leaf elemental concentrations after the fertilization. Leaf N:P ratios showed considerable differences among co-occurring species. Overall, we found that soil N addition treatments increased leaf N concentration, although leaf N:P ratios were not affected. Changes in leaf Al, Fe and S concentrations were correlated with species functional strategy: conservative species showed a greater increase in leaf Fe compared with acquisitive species, whereas acquisitive species showed a greater increase in leaf Al but a decrease in leaf S compared with conservative species. Synthesis. We show that soil elements uptake differs between acquisitive and conservative species and that acquisitive species may not take up soil elemental resources more effectively than conservative species. We suggest that the greater Fe acquisition by conservative species, in comparison to acquisitive species, might be due to a stress tolerance strategy. The overall increase in leaf N showed that, in this nutrient-poor forest, N is a fundamental requirement irrespective of species functional strategies. Given the increased leaf Al and Fe concentration after liming, we also suggest that these elements are important, and possibly limiting (Fe), in this heath forest.