© 2007 Heron Publishing—Victoria, Canada
Removal of nutrient limitations by long-term fertilization decreases nocturnal water loss in savanna trees
Fabian G. Scholz (1), 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 Ecología, Genética y Evolución, 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 (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 Brasília, Caixa Postal 04457 Brasília, DF 70904-970, Brazil / 6. Department of Civil and Environmental Engineering. Florida International University, 10555 W. Flagler Street, EC 3680, Miami,
FL 33174, USA
/ Received March 16, 2006; accepted June 23, 2006; published online January 2, 2007
Summary
Under certain environmental conditions, nocturnal transpiration can be relatively high in temperate and tropical woody species.
We have previously shown that nocturnal sap flow accounts for up to 28% of total daily transpiration in woody species growing
in a nutrient-poor Brazilian Cerrado ecosystem. In the present study, we assessed the effect of increased nutrient supply
on nocturnal transpiration in three dominant Cerrado tree species to explore the hypothesis that, in nutrient-poor systems,
continued transpiration at night may enhance delivery of nutrients to root-absorbing surfaces. We compared nocturnal transpiration
of trees growing in unfertilized plots and plots to which nitrogen (N) and phosphorus (P) had been added twice yearly from
1998 to 2005. Three independent indicators of nocturnal transpiration were evaluated: sap flow in terminal branches, stomatal
conductance (gs), and disequilibrium in water potential between covered and exposed leaves (ΔΨL). In the unfertilized trees, about 25% of the total daily sap flow occurred at night. Nocturnal sap flow was consistently
lower in the N- and P-fertilized trees, significantly so in trees in the N treatment. Similarly, nocturnal gs was consistently lower in fertilized trees than in unfertilized trees where it sometimes reached values of 150 mmol m–2 s–1 by the end of the dark period. Predawn gs and the percentage of nocturnal sap flow were linearly related. Nocturnal ΔΨL was significantly greater in the unfertilized trees than in N- and P-fertilized trees. The absolute magnitude of ΔΨL increased linearly with the percentage of nocturnal sap flow. These results are consistent with the idea that enhancing nutrient
uptake by allowing additional transpiration to occur at night when evaporative demand is lower may avoid excessive dehydration
associated with increased stomatal opening during the day when evaporative demand is high.
Keywords:
Cerrado, leaf water potential, stomatal conductance, transpiration.
