AbstractTwo evergreen species - Eucalyptus tetrodonta and E. miniata, two deciduousspecies - Terneinaliaferdinand/ana and Planchonia careya and one partly deciduous species - Syzygiune suburb/cu/are were sampled at a savanna site at CSIRO, Berrimah, near Darwin in the Northern Territory of Australia. Newly expanded leaves of the deciduous and evergreen species, and old leaves of the partly deciduous and evergreen species were sampled. Gas exchange measurements (assimilation at light saturation, stomatal conductance and rate of dark respiration) were made on a minimum of six leaves of five or six trees of each species. Leaves were then collected for chemical analysis and calculation of construction and maintenance costs, nitrogen use efficiency and instantaneous transpiration efficiency.
Evergreen species had significantly lower specific leaf area and leaf nitrogenand ash content, but significantly higher heat of combustion and crude fat content compared to deciduous species. Light saturated assimilation rate was higher for deciduous species when considered on a leaf dry weight basis but higher for evergreen species when considered on a leaf area basis, due to differences in specific leaf area. Stomatal conductance was significantly higher for evergreen species compared to deciduous species. Instantaneous transpiration efficiency was significantly higher for deciduous species compared to evergreen species, but nitrogen use efficiency was not significantly different. Leaf construction cost was always significantly higher for evergreen species compared to deciduous species, but maintenance costs were not significantly different.
Australian tropical savannas show remarkable diversity of phenological strategies which allow different species to coexist. Species with longer leaf life spans have a higher ratio of cost:benefit (leaf construction cost:assimilation rate at light saturation) compared to species with shorter leaf life spans, confirming work in a South American savanna. Deciduous and evergreen species are able to coexist in tropical savannas because they partition resources both temporally and spatially in order to reduce interspecific competition.
|Date of Award||May 1996|
|Supervisor||Derek Eamus (Supervisor)|