Temporal dynamics of stem expansion and contraction in savanna trees: withdrawal and recharge of stored water
Fabian C. Scholz (1, 2), Sandra J. Bucci (1, 2), Guillermo Goldstein (1, 2, 3), Frederick C. Meinzer (4), Augusto C. Franco (5) and Fernando Miralles-Wilhelm (6)
1. Laboratorio de Ecología Funcional, Departamento de Ecologia, Genetica y Evolucion, Facultad de Ciencias Exactas y Naturales,
Universidad de Buenos Aires, Ciudad Universitaria, Nuñez, Buenos Aires, Argentina / 2. Department of Biology, University of Miami, P.O. Box 249118, Coral Gables, FL 33124, USA / 3. Corresponding author () / 4. USDA Forest Service, Forestry Sciences Laboratory, 3200 SW Jefferson Way, Corvallis, OR 97331, USA / 5. Departamento de Botanica, Universidade de Brasília, Caixa Postal 04357 Brasília, DF 70919-970, Brazil / 6. Department of Civil and Environmental Engineering, Florida International University, 10555 W. Flagler Street, EC 3680, Miami,
FL 33174, USA / Received January 8, 2007; accepted February 5, 2007; published online January 2, 2008
Summary
Relationships between diel changes in stem expansion and contraction and discharge and refilling of stem water storage tissues
were studied in six dominant Neotropical savanna (cerrado) tree species from central Brazil. Two stem tissues were studied,
the active xylem or sapwood and the living tissues located between the cambium and the cork, made up predominantly of parenchyma
cells (outer parenchyma). Outer parenchyma and sapwood density ranged from 320 to 410 kg m–3 and from 420 to 620 kg m–3, respectively, depending on the species. The denser sapwood tissues exhibited smaller relative changes in cross-sectional
area per unit change in water potential compared with the outer parenchyma. Despite undergoing smaller relative changes in
cross-sectional area, the sapwood released about 3.5 times as much stored water for a given change in area as the outer parenchyma.
Cross-sectional area decreased earlier in the morning in the outer parenchyma than in the sapwood with lag times up to 30
min for most species. The relatively small lag time between dimensional changes of the two tissues suggested that they were
hydraulically well connected. The initial morning increase in basal sap flow lagged about 10 to 130 min behind that of branch
sap flow. Species-specific lag times between morning declines in branch and main stem cross-sectional area were a function
of relative stem water storage capacity, which ranged from 16 to 31% of total diurnal water loss. Reliance on stored water
to temporarily replace transpirational losses is one of the homeostatic mechanisms that constrain the magnitude of leaf water
deficits in cerrado trees.
Keywords:
capacitance, cerrado, electronic dendrometers, plant-water relations, sap flow, sapwood.
