Chun-Ta Lai, San Diego State University, Jean Ometto, Centro de Energia Nuclear na Agricultura, Brazil, Luiz A. Martinelli, University of Sao Paulo, Brazil, Joe Berry, Stanford University, Tomas Domingues, The University of Edinburgh, and James R. Ehleringer, University of Utah.
We measured
oxygen isotope ratios (d18O) of leaf and stem water from a suite of major functional
types in Amazonian forests
and pastures to investigate
diel patterns of isotopic leaf water enrichment (Do) in March and September 2004 as part of the Large-Scale Biosphere
Atmosphere Project (LBA), an international effort to better understand
ecosystem processes at regional scales in the Amazon Basin. Two experiments were conducted
separately: one in the wet season (March) and the other in the dry season (September).
During each field experiment, leaf and stem samples were collected on two-hour
intervals at night and hourly during the day for a total of 50 hours from six
species in the forest and two species in a pasture, representing four major
functional types in the Amazonia, including overstory trees and lianas, lower canopy trees and lianas in the forest and C4 grasses and C3 shrubs in the pasture. Measured Do
showed similar diel variations
between the two species in the pasture while considerable variations were
observed among the six species in the forest. Physiological and gas exchange
properties, including leaf water content and stomatal conductance, also were
measured at times representing the two seasons in order to predict isotopic
leaf water enrichment using three different models that considered either
steady state or non-steady state description. Species-specific and
environmental factors that influence predictions of Do
with respect to these models are discussed.
