Much of the rainfall in the Amazon basin is
recycled; i.e. precipitation is evapo-transpired back to the atmosphere
where it's re-precipitated. Crucial to conservation issues is whether
the primary conduit of vapor from the forest to the atmosphere is via
transpiration or evaporation. Obviously, if it's transpiration, loss
of forested areas can have significant impact on climate. Using stable
isotope techniques we were able to trace the source of vapor and observed
that 70 to 100% of the vapor generated by the forest is via transpiration.
The uptake of water by tropical tree roots is
also a subject of interest in my laboratory, especially under the possibility
of severe dry season brought about by climate change.The coexistence
of woody species and grasses in savannas is thought to be possible because
these two growth forms exploit different soil compartments for moisture.
Grasses exploit the shallower layers of the soil profile and are dormant
during the dry season, whereas woody species exploit the deeper layers
of the soil profile and remain active during the dry season. In Amazonian
abandoned pastures, which resemble savannas, we observed the opposite.
Colonizer woody species actually seem to be acquiring water from shallower
layers of the soil profile compared to grasses. Another factor which
may complicate this two compartment system is hydraulic lift. Hydraulic
lift is the redistribution of water in the soil profile through the
plant root system. We have observed hydraulic lift for two species commonly
found in the Brazilian savanna (cerrado), but need to determine its
actual importance in the ecosystem water budget.
Sample Publications
Moreira MZ, Sternberg L, Martinelli
LA, Victoria RL, Barbosa EM, Bonates LCM, Nepstad DC. Contribution of
transpiration to forest ambient vapor based on isotopic measurements.
Global Change Biology. 3:439-450. 1997.
Moreira M., Sternberg L da SL,
Nepstad D. Vertical patterns of soil water uptake by plants in a primary
forest and an abandoned pasture in the Eastern Amazon: an isotopic approach.
Plant and Soil 222: 95-107.
2000.
Sternberg L. da S.L, Moreira M.
Z. and Nepstad D. Uptake of water by lateral roots of small trees and
saplings in an Amazonian tropical forest. Plant
and Soil 238:151-158. 2002.
Nepstad D.C., Moutinho P., Dias- Filho M.B.,
Davidson E., Cardinot G., Markewitz D., Figueiredo R., Vianna N., Lefebvre
P., Chambers J., Sternberg L., Moreira M., Guerreiros J.B., Barros L.,
Ishida F.Y., Belk E. and Schwalbe K. (2002) The effects of rainfall
exclusion on canopy processes and biogeochemistry of an Amazon forest.
Journal of Geophysical Research 107(53):1-18. 2002.
Moreira M. Z., Scholz, F. G., Bucci S. J., Sternberg
L. da S. L., Goldstein G., Meinzer F. C. and Franco A. C. Hydraulic
lift in a Netropical Savanna.
Functional Ecology 17:573-581. 2003.
Romero -Saltos H, Sternberg L da SL, Moreira
MZ, Nepstad DC. Rainfall exclusion in an eastern Amazonian forest alters
soil water movement and depth of water uptake. American
Journal of Botany 92: 443-445. 2005.
Sternberg, L da SL, Bucci S, Franco A, Goldstein
G, Hoffman WA, Meinzer FC, Moreira MZ, Scholz F. Long range lateral
root activity by neo-tropical savanna trees. Plant
and Soil 270: 169-178. 2005.
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