Drought-tolerance of an eastern Amazon forest, recovery of canopy water status: results from a throughfall exclusion experiment.
Gina
Knust
Cardinot, UFRJ/IPAM, cardinot@ipam.org.br
(Presenting)
Daniel
Curtis
Nepstad, WHRC/IPAM, dnepstad@whrc.org
N.
Michele
Holbrook, Harvard University, holbrook@oeb.harvard.edu
David
Ray, WHRC, dray@whrc.org
Evergreen forest canopies are able to persist during the extended dry season in east central Amazonia because a favorable water balance can be maintained. However, the adaptations that make this possible are not well understood. Over the past four years we have been monitoring changes in predawn leaf water potentials (Yp; 7 paired species), leaf area index (LAI), and plant available soil water (PAW) in the rainfall exclusion experiment (Santarem, Para, Brazil). The study consists of two 1-ha plots, a control and treatment plot from which rainfall wet season (6-mos) water inputs have been reduced by 50% since 2000. Strong differences in Yp were first detected during the 2001 dry season, when average Yp values were more negative (-1.62 MPa) in the treatment plot, approximately 2 times that of the control plot (-0.85MPa). By this time PAW from 0-11 m deep had declined by 55%, and LAI by 13%, in the treatment relative to the control plot. A response in Yp of similar magnitude was observed during the following dry seasons (2002/03), even as PAW became further depleted. LAI was 25% lower in the treatment than control plot during the 2003 dry season. Surprisingly, Yp has consistently recovered to background levels in treatment plot during each subsequent wet season. In addition to reducing total LAI, trees in the treatment plot have produced smaller leaves, and we have detected some evidence of water uptake via leaf surfaces, suggesting some mechanisms this vegetation relies on to cope with drought stress.
Submetido por Gina Knust Cardinot em 18-MAR-2004
Tema Científico do LBA: CD (Armazenamento e Trocas de Carbono)