© 2004 Heron Publishing—Victoria, Canada
Functional convergence in hydraulic architecture and water relations of tropical savanna trees: from leaf to whole plant
S. J. Bucci (1), G. Goldstein (2, 3), F. C. Meinzer (4), F. G. Scholz (2), A. C. Franco (5) and M. Bustamante (6)
1. Department of Biology, University of Miami, Coral Gables, FL 33124, USA / 2. Laboratorio de Ecología Funcional, Departamento de Ciencias Biológicas, Facultad de Ciencias Exactas y Naturales, Universidad
de Buenos Aires, Ciudad Universitaria, Nuñez, Buenos Aires, Argentina / 3. Corresponding author (goldstein@bio.miami.edu) / 4. USDA Forest Service, Forestry Sciences Laboratory, 3200 SW Jefferson Way, Corvallis, OR 97331, USA / 5. Departamento de Botanica, Universidade de Brasilia, caixa postal 04457, Brasilia, DF 70919970, Brazil / 6. Departamento de Ecología, Universidade de Brasilia, caixa postal 04457, Brasilia, DF 70919970, Brazil / Received August 11, 2003; accepted March 8, 2004; published online June 1, 2004
Summary
Functional convergence in hydraulic architecture and water relations, and potential trade-offs in resource allocation were
investigated in six dominant neotropical savanna tree species from central Brazil during the peak of the dry season. Common
relationships between wood density and several aspects of plant water relations and hydraulic architecture were observed.
All species and individuals shared the same negative exponential relationship between sapwood saturated water content and
wood density. Wood density was a good predictor of minimum (midday) leaf water potential and total daily transpiration, both
of which decreased linearly with increasing wood density for all individuals and species. With respect to hydraulic architecture,
specific and leaf-specific hydraulic conductivity decreased and the leaf:sapwood area ratio increased more than 5-fold as
wood density increased from 0.37 to 0.71 g cm–3 for all individuals and species. Wood density was also a good predictor of the temporal dynamics of water flow in stems,
with the time of onset of sap flow in the morning and the maximum sap flow tending to occur progressively earlier in the day
as wood density increased. Leaf properties associated with wood density included stomatal conductance, specific leaf area,
and osmotic potential at the turgor loss point, which decreased linearly with increasing wood density. Wood density increased
linearly with decreasing bulk soil water potential experienced by individual plants during the dry season, suggesting that
wood density was greatest in individuals with mostly shallow roots, and therefore limited access to more abundant soil water
at greater depths. Despite their taxonomic diversity and large intrapopulation differences in architectural traits, the six
co-occurring species and their individuals shared similar functional relationships between all pairs of variables studied.
Thus, rather than differing intrinsically in physiological responsiveness, the species and the individuals appeared to have
distinct operating ranges along common physiological response curves dictated by plant architectural and structural features.
The patterns of water uptake and access to soil water during the dry season appeared to be the main determinant of wood density,
which constrained evolutionary options related to plant water economy and hydraulic architecture, leading to functional convergence
in the neotropical savanna trees studied.
Keywords:
cerrado, hydraulic conductivity, sap flow, soil water potential, water transport, wood density.
