Drought tolerance of Amazon trees reflects a low vulnerability to cavitation: results from a large scale rainfall exclusion experiment.
Gina
Knust
Cardinot, UFRJ/IPAM, cardinot@ipam.org.br
(Presenting)
N.
Michele
Holbrook, Harvard University, holbrook@oeb.harvard.edu
Daniel
Curtis
Nepstad, WHRC/IPAM, dnepstad@whrc.org
The capacity of xylem to transport water from the soil to the leaves is itself at risk during periods of drought due to the increased potential for cavitation. Our research focuses on the effects of drought on the water transport capacity of Amazonian rainforest trees. Our goal is to understand the extent to which cavitation results in a loss of hydraulic conductivity, potentially leading to stomatal closure, leaf shedding, and tree death. Our research was carried out within the context of the world’s largest rainfall exclusion experiment. This experiment, the first conducted in a rainforest (eastern Amazonia; Para State/Brazil) consists of two 1-ha plots, of which one is a control and one in which rainfall reaching the forest floor has been reduced by 50% since 2000. We measured xylem hydraulic conductivity using a field pressure-drop flow meter to test the hypothesis that cavitation limits water uptake from deep soil layer. We chose four species which are common in this area. Our preliminary results indicate that the specific conductivity (Ks) of branches did not differ significantly between plots for all studied species. Vulnerability curves in branches showed a high tolerance to cavitation (50% loss of hydraulic conductivity at values smaller than -3.5MPa), consistent with the lack of an impact of imposed drought on xylem hydraulic conductivity. The possibility that water uptake by leaves (instead of through the soil) could play an important role in the water balance of these trees might be responsible for these findings. Drought tolerance exhibited by Amazon tropical rainforest trees allows them to maintain physiological function and xylem continuity despite the marked seasonality in rainfall in the eastern Amazon.
Submetido por Gina Knust Cardinot em 18-MAR-2004
Tema Científico do LBA: LC (Mudanças dos Usos da Terra e da Vegetação)