Document: PAU-3-32-11

Partitioning of soil water among tree species in a Brazilian Cerrado ecosystem.

JACKSON, P.C.* ¹, F.C.MEINZER ², M.BUSTAMANTE ³, G.GOLDSTEIN ⁴, A.FRANCO ⁵, P.W.RUNDEL ⁶, L.CALDAS ⁵, E.IGLER ⁷ and F.CAUSIN ⁷

Kennesaw State University ¹
Hawaii Agriculture Research Center ²
Universidad de Brasilia ³
University of Hawaii ⁴
Universidad de Brasilia ⁵
University of California, Los Angeles ⁶
FCEN, Universidad de Buenos Aires. ⁷

Abstract:
Source water used by woody perennials in a Brazilian savanna (Cerrado) was determined by comparing the stable hydrogen isotope composition (D) of xylem sap and soil water at different depths during two consecutive dry seasons (1995 and 1996). Plant water status and rates of water use were also determined and compared with xylem water D values. Overall, soil water D decreased with increasing depth in the soil profile. Mean D values were -35 for the upper 170 cm of the soil and -55 between 230 and 400 cm depth at the end of the 1995 dry season. Soil water content increased with depth, from 18% near the surface to about 28% at 400 cm. A similar pattern of decreasing soil water D with increasing depth was observed at the end of the 1996 dry season. Patterns consistent with hydraulic lift were observed in soil profiles sampled in 1995 and 1996. Concurrent analyses of soil and xylem water D values indicated a distinct partitioning of water resources among 10 representative woody species (five deciduous and five evergreen). Among these species, four evergreen and one deciduous species acquired water primarily in the upper soil layers (above 200 cm), whereas three deciduous and one evergreen species tapped deep sources of soil water (below 200 cam). One deciduous species exhibited intermediate behavior. Total daily sapflow was negatively correlated with xylem sap D values indicating that species with higher rates of water use during the dry season tended to rely on deeper soil water sources. Among evergreen species, minimum leaf water potentials were also negatively correlated with xylem water D values, suggesting that access to more readily available water at greater depth permitted maintenance of a more favorable plant water status. No significant relationship between xylem water D and plant size was observed in two evergreen species, suggesting a strong selective pressure for small plants to rapidly develop a deep root system. The degree of variation in soil water partitioning, leaf phenology and leaf longevity was consistent with the high diversity of woody species in the Cerrado.

Keywords: deciduous, deuterium, evergreen, hydraulic lift, neotropical savanna, resource partitioning, roots, stable hydrogen isotope composition

This abstract is being presented at: 1:00 PM in session:
Oral Session #34: Water Relations in Trees.