Hydraulic redistribution in Neotropical savannas woody species

SCHOLZ FABIÁN G., BUCCI SANDRA J., GOLDSTEIN GUILLERMO, MEINZER FREDERICK C.,

Edinburgo

Conferencia; International Conference Tropical Savannas & Seasonally dry forest; 2003

The magnitude and direction of water transport by roots of evergreen, brevideciduous and deciduous dominant Brazilian savanna (Cerrado) woody species was determined with a heat-pulse system that allowed bi-directional measurements of sap flow. Soil water potentials and environmental variables were also monitored during the dry season and during the dry to wet season transition in a Cerrado site near Brasilia. Byrsonima crassa has dimorphic root system with many shallow lateral roots and only one major tap root. The patterns of sap flow observed during the dry season was consistent with the occurrence of hydraulic redistribution of soil water, the movement of water from moist to drier regions of the soil profile via plant roots.  Shallow roots exhibited positive sap flow (from the soil into the plant) during the day and negative sap flow (from the plant into the soil) at night. At the peak of the dry season, when water potentials near the upper part of the soil profile were about -2.5 MPa, some lateral roots exhibited 114 cm3 of reverse flow (from roots to soil) during the night, which represented 14% of the total daily sap flow measured at the base of the trunk. At the beginning of the wet season, and after soil water potentials of the entire soil profile reached near 0 MPa , the same lateral roots exhibited a positive nighttime sap flow (from soil to stem xylem) of 300 cm3, which represents 23% of the total daily sap flow. The tap root contributed only 5% of the total sap flow of the plant during periods of high evaporative demand. Results from other species and the relationships between sap flow directions and environmental conditions will be discussed.