<S1-13> Depth of water uptake and flowering frequency of dipterocarp trees

Abstract

Irregular drought has been reported to trigger general flowering (GF) in lowland tropical rain forests in Southeast Asia. We hypothesized that the interspecific differences in water uptake depth may influence the flowering frequency and timing in GF among tree species. We compared the flowering peaks between high- and low-frequency flowering trees based on the phenology data during 1993-2011. As expected, the flowering peak of high-frequency flowering species preceded that of low-frequency species. The soil water sources of the dipterocarp trees were assessed using oxygen stable isotope composition (δ18O) with snap- and sequence-shot methods. Although both an unclear vertical profile of soil water δ18O and the short sampling term made it difficult to estimate the water uptake depth using either method, δ18O of dipterocarp trees is likely influenced by flowering frequency. However, an accurate estimation of vertical pattern of soil water use by tropical trees will be required to fully test this hypothesis.