Seasonal Variation in Water Relations of Trees of Differing Leaf Phenology in a Wet - Dry Tropical Savanna near Darwin, Northern Australia

Abstract

The seasonal variation in leaf xylem pressure potential at dawn (ψdawn), leaf tissue water characteristics and daily maximum leaf conductance was measured in eight woody species in a wet–dry tropical savanna near Darwin, northern Australia, between October 1992 and October 1993. The species were Eucalyptus miniata, E. tetrodonta, E. clavigera, Xanthostemon paradoxus, Erythrophleum chlorostachys, Planchonia careya, Terminalia ferdinandiana and Cochlospermum fraseri. The species represented the major leaf phenological types, evergreen, semi-deciduous and fully deciduous. The climate of the region is characterised by annual drought during the winter months, when virtually no rain falls and vapour pressure deficit (VPD) in the afternoon reaches 3 kPa for 5 consecutive months each year. Despite this drought, ψdawn remained high (–1.3 to –1.5 MPa in evergreen species and –0.5 to –1.5 MPa in deciduous species) relative to those trees that experience summer drought in temperate and arid Australia. There was a tendency for evergreen and semi-deciduous species to maintain positive turgor to lower xylem pressure potentials (mean osmotic potential at incipient plasmolysis, π0 = –2.15 MPa) than the fully deciduous species (π0 = –2.03 MPa). For all species, the daily maximum leaf conductance (gmax) was maximal in the wet and decreased during the dry season. Diurnally, (gmax occurred near midday in the wet season, but at about 0800–1000 hours during the dry season and the ‘buildup’, the transitional period between the dry and wet seasons. There was substantial decrease in (gmax (from 650–1000 mmol m-2 s-1 in March to 200 mmol m-2 s-1 in May) early in the dry season in two of the three fully deciduous species (Planchonia careya and Cochlospermum fraseri). The dominant evergreen species Eucalyptus miniata, by contrast, had high gmax (> 400 mmol m-2 s-1) throughout the dry season, suggesting it had access to groundwater. For each species, gmax declined with decreasing dawn water potential in a log-linear manner; the slope of this relationship tended to increase with increasing degree of deciduousness.

Seasonal changes in hydraulic conductance, xylem embolism and leaf area in Eucalyptus tetrodonta and Eucalyptus miniata saplings in a north Australian savanna

“…Values for all three Eucalyptus species are within the range reported for temperate angiosperm trees (Patiño et al 1995), and higher than those reported for other evergreen trees from savannas or dry tropical forests (Goldstein, Rada & Catalan 1987;Sobrado 1993Sobrado , 1996Sobrado , 1997. Mature eucalypt trees in savanna near Darwin are able to access subsoil moisture throughout the dry season (Myers et al 1997;O'Grady et al 1999), and consequently maintain high rates of sap flow, which are facilitated by conductive xylem. Trees from drier habitats, such as Venezuelan dry tropical forest, tend to have smaller, less conductive vessels (Tyree et al 1994).…”

“…Mature trees maintain high leaf water potentials and high rates of assimilation, transpiration and leaf flushing during the dry season (Myers et al 1997;Williams et al 1997b;Myers et al 1998; O'Grady, Eamus & Hutley 1999;Eamus et al 1999). However, in saplings, leaf water potentials, stomatal conductance, transpiration and assimilation rates all decline (Prior, Eamus & Duff 1997;Prior & Eamus 1999).…”

“…ex Schauer is an evergreen tree often codominant with E. tetrodonta (Brock 1993). Mature trees of the two species have similar leaf water potentials, stomatal conductance and rates of assimilation and transpiration and patterns of growth throughout the year (Myers et al 1997;O'Grady et al 1999;Eamus et al 1999). However, E. miniata saplings may grow faster and more consistently than E. tetrodonta saplings.…”

Seasonal changes in carbohydrates, cyclitols, and water relations of 3 field grown Eucalyptus species from contrasting taxonomy on a common site

“…Predawn water potentials measured in this study fall within the values commonly obtained from field based studies in Eucalyptus (Myers et al, 1997;White et al, 1999;Zubrinich et al, 2000). The slight reductions in predawn water potential Ψ of 0.3-0.5 MPa observed for all species from winter to summer may indicate mild water deficit at this site in summer, as could be expected from the Mediterranean rainfall patterns.…”

Plant- and stand-level variation in biophysical and physiological traits along tree density gradients in the Cerrado

“…Several studies have characterized the effects of seasonal changes in soil water availability and evaporative demand on regulation of leaf water status in woody plants from tropical savannas and other tropical and subtropical habitats (e.g. Eamus and Cole, 1997;Duff et al, 1997;Myers et al, 1997;Franco, 1998;Meinzer et al, 1999;Thomas and Eamus, 2002;McClenahan et al, 2004;Prado et al, 2004;Bucci et al, 2005). Fewer studies have focused on characterizing biophysical properties governing functional traits related to tree hydraulic architecture (e.g.…”