SEASONAL TRENDS IN CARBON ASSIMILATION, STOMATAL CONDUCTANCE, PRE-DAWN LEAF WATER POTENTIAL AND GROWTH IN TERMINALIA-FERDINANDIANA, A DECIDUOUS TREE OF NORTHERN AUSTRALIAN SAVANNAS
Ld. Prior et al., SEASONAL TRENDS IN CARBON ASSIMILATION, STOMATAL CONDUCTANCE, PRE-DAWN LEAF WATER POTENTIAL AND GROWTH IN TERMINALIA-FERDINANDIANA, A DECIDUOUS TREE OF NORTHERN AUSTRALIAN SAVANNAS, Australian Journal of Botany, 45(1), 1997, pp. 53-69
Seasonal trends in pre-dawn leaf water potential and morning and after
noon rates of light-saturated assimilation and stomatal conductance we
re studied in saplings of the deciduous tree Terminalia ferdinandiana
Excell. Mean daily maximum assimilation rates ranged from 11 mu mol m(
-2) S-1 in the wet season to 8 mu mol m(-2) s(-1) during the transitio
n from the wet to the dry season. Saplings were without leaves from Ju
ne to October inclusive (dry season). There was a log-linear relations
hip between stomatal conductance and pre-dawn leaf water potential (r
= 0.76, n = 325), and a weak linear relationship between daily maximum
assimilation and pre-dawn leaf water potential (r = 0.39, n = 184). A
ssimilation rates were higher in the morning than in the afternoon in
April and May, but were similar throughout the day from December to Ma
rch. Seasonal trends in assimilation could be attributed primarily to
stomatal closure, but diurnal differences could not. High leaf tempera
tures may have been responsible for observed lower assimilation rates
in the afternoon in April and May. Assimilation and stomatal conductan
ce decreased when leaf temperatures rose above 38 degrees C and/or the
leaf-to-air vapour pressure difference exceeded 4-4.5 kPa. Pre-dawn l
eaf water potentials decreased more quickly, and stomatal conductance
was more sensitive to this decrease, in T. ferdinandiana saplings than
in saplings of Eucalyptus tetrodanta F.Muell. a co-occurring evergree
n tree. Specific leaf area and assimilation per unit dry weight were h
igher in T. ferdinandiana than in E. tetrodonta which is consistent wi
th other studies of costs and benefits of deciduousness.