Rafael
S
Oliveira, University of California - Berkeley, rafaels@socrates.berkeley.edu
(Presenting)
Todd
E
Dawson, UC Berkeley, tdawson@socrates.berkeley.edu
Stephen
O
Burgess, University of Western Australia, ssb@cyllene.uwa.edu.eau
Daniel
Curtis
Nepstad, Woods Hole research center, dnepstad@whrc.org
About half of the Amazon rainforest is subject to seasonal drought. However, several studies have documented that these forests, under a strongly seasonal climate, do not become water stressed during the dry season. In addition to deep soil water uptake, another contributing explanation for the absence of plant water stress during drought is the occurrence of hydraulic redistribution, the nocturnal transfer of water by roots from moister to drier regions in the soil profile. Here, we present patterns of sap flow in roots of 3 dimorphic-rooted species in the Tapajós Forest that are consistent with the occurrence of hydraulic redistribution. We measured sap flow in lateral and tap roots of our 3 study species over a 2-year period using the heat ratio method, a sap flow technique that allows bi-directional measurement of water flow. On certain nights during the dry season, reverse or acropetal flow (i.e. in the direction of the soil) in the lateral roots and positive or basipetal sap flow in the tap roots of Coussarea racemosa (caferana), Manilkara huberi (maçaranduba) and Protium sp. (breu) were observed, a pattern consistent with upward hydraulic redistribution (hydraulic lift). With the onset of heavy rains, we observed continuous nighttime reversals in sap-flow in the tap root, and positive sap flow in lateral roots, indicating water movement from wet top soil to deeper soils (downward hydraulic redistribution). Both patterns were documented in trees within a rainfall exclusion plot (Seca Floresta) and also in the control plot. Hydraulic redistribution may help facilitate seedling recruitment and tree survival under extreme water deficits. Therefore, our findings have fundamental implications for understanding the linkage between tree function and forest function as driven by plant response to drought.
Submetido por Rafael Silva Oliveira em 17-MAR-2004
Tema Científico do LBA: SH (Hidrologia e Química das Águas)