© 2006 Heron Publishing—Victoria, Canada
Seasonal patterns of leaf gas exchange and water relations in dry rain forest trees of contrasting leaf phenology
Brendan Choat (1, 2, 5, 6), Marilyn C. Ball (2), Jon G. Luly (3), Christine F. Donnelly (4) and Joseph A. M. Holtum (1)
1. Department of Tropical Plant Science, James Cook University, Townsville, Queensland 4811, Australia / 2. Research School of Biological Sciences, Australian National University, Canberra, Australian Capital Territory 2601, Australia / 3. School of Tropical Environment Studies and Geography, James Cook University, Townsville, Queensland 4811, Australia / 4. Statistical Consulting Unit, Australian National University, Canberra, Australian Capital Territory 2601, Australia / 5. Department of Viticulture and Enology, University of California, 1 Shields Ave., Davis, CA 95616, USA / 6. Corresponding author (bchoat@ucdavis.edu) / Received December 14, 2004; accepted September 27, 2005; published online February 1, 2006
Summary
Diurnal and seasonal patterns of leaf gas exchange and water relations were examined in tree species of contrasting leaf phenology
growing in a seasonally dry tropical rain forest in north-eastern Australia. Two drought-deciduous species, Brachychiton australis (Schott and Endl.) A. Terracc. and Cochlospermum gillivraei Benth., and two evergreen species, Alphitonia excelsa (Fenzal) Benth. and Austromyrtus bidwillii (Benth.) Burret. were studied. The deciduous species had higher specific leaf areas and maximum photosynthetic rates per
leaf dry mass in the wet season than the evergreens. During the transition from wet season to dry season, total canopy area
was reduced by 70–90% in the deciduous species and stomatal conductance (gs) and assimilation rate (A) were markedly lower in the remaining leaves. Deciduous species maintained daytime leaf water potentials (ΨL) at close to or above wet season values by a combination of stomatal regulation and reduction in leaf area. Thus, the timing
of leaf drop in deciduous species was not associated with large negative values of daytime ΨL (greater than –1.6 MPa) or predawn ΨL (greater than –1.0 MPa). The deciduous species appeared sensitive to small perturbations in soil and leaf water status that
signalled the onset of drought. The evergreen species were less sensitive to the onset of drought and gs values were not significantly lower during the transitional period. In the dry season, the evergreen species maintained their
canopies despite increasing water-stress; however, unlike Eucalyptus species from northern Australian savannas, A and gs were significantly lower than wet season values.
Keywords:
CO2 assimilation, deciduous, dry tropical forest, evergreen, stomatal conductance, water potential.
