HR: 10:50h
AN: B22B-03    [Abstracts]
TI: Diel Variations Of Leaf Water Oxygen Isotope Ratios In Tropical Forest And Pasture Vegetation Of The Amazon Are Consistent With Non-Steady-State-Model Predictions
AU: * Ometto, J P
EM: jpometto@cena.usp.br
AF: Centro de Energia Nuclear na Agricultura, Av Centenario, 303, Piracicaba, SP 13400-970 Brazil
AU: Ehleringer, J R
EM: ehleringer@biology.utah.edu
AF: University of Utah, 257S 1400E, Salt Lake City, UT 84112 United States
AU: Martinelli, L A
EM: martinelli@cena.usp.br
AF: Centro de Energia Nuclear na Agricultura, Av Centenario, 303, Piracicaba, SP 13400-970 Brazil
AU: Berry, J
EM: joeberry@globalecology.stanford.edu
AF: Carnegie Institute of Washington, 260 Panama St, Stanford, CA 94305 United States
AU: Lai, C
EM: lai@biology.utah.edu
AF: University of Utah, 257S 1400E, Salt Lake City, UT 84112 United States
AB: We evaluated diel variations in the ²H and ¹⁸O of leaf and source water for vegetation within a primary forest and a pasture in eastern Brazilian Amazonia. During both the dry and wet seasons of 2004, we collected leaf water, stem water, and atmospheric water every 1-2 hours during 3-day intensive field campaigns. Leaf water isotope enrichment for upper canopy trees and lianas in the rainforest showed a significant fit to a non-steady state transient model developed by Cernuzack et al. (2002). The adequate fitting of measured data to the model contrasted with isotope values predicted by a steady-state Craig-Gordon model particularly for early morning and evening time periods. These filed observations suggest a longer leaf-water isotopic equilibration period for tropical vegetation than has previously been considered. In contrast, leaf water isotope ratios of C4 pasture grasses showed a strong fit with the steady state model, suggesting that time lags were much reduced in this vegetation type. Diurnal fluctuations in the oxygen isotope ratio of leaf water in rainforest vegetation during the dry season varied from 0‰ to +16‰ and -6‰ to +28‰, for oxygen and hydrogen isotopes, respectively. Isotopic enrichment of leaf water in grasses during the same period was greater. The hydrogen and oxygen isotope ratio variations during the wet season were greatly reduced when compared to dry season patterns. These applications of these observations to partitioning carbon dioxide fluxes in both vegetation types are discussed.
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1851 Plant ecology (0476)
DE: 4227 Diurnal, seasonal, and annual cycles (0438)
SC: Biogeosciences [B]
MN: Fall Meeting 2005