A COST-BENEFIT-ANALYSIS OF LEAVES OF 4 AUSTRALIAN SAVANNA SPECIES

We conducted a cost-benefit analysis of the contrasting phenologies of two evergreen and two deciduous species of the savannas of north Aust ralia. Stomatal conductance, rates of light-saturated assimilation (A( max)) and dark respiration were measured for six leaves from each of f ive or six trees. These leaves were then analyzed for total nitrogen, ether-soluble lipids, ash content, and heat of combustion. Constructio n and maintenance costs, nitrogen-use efficiencies and instantaneous t ranspiration efficiencies were then calculated from these data. Evergr een species had significantly lower specific leaf area, leaf nitrogen and leaf ash content than deciduous species. Evergreen species also ha d significantly higher heat of combustion and lipid content of crude e xtracts than deciduous species. Light-saturated assimilation rates wer e higher in evergreen species on a leaf area basis, but were higher in deciduous species on a leaf dry weight basis. In both evergreen and d eciduous species, A(max) and total Kjeldahl nitrogen were linearly rel ated. Similarly, nitrogen-use efficiency did not differ among species. Leaf construction costs were significantly higher for evergreen speci es than for deciduous species, but maintenance costs did not differ am ong species. Evergreen species had a higher cost:benefit ratio than de ciduous species but because of their longer-lived leaves, the payback interval was longer in evergreen species than in deciduous species. Th ese results support the hypotheses that: (1) longer-lived leaves are m ore expensive to construct than shorter-lived leaves, and (2) there is a higher investment of nitrogen into short-lived leaves to support a higher A(max) over a shorter payback interval. We conclude that decidu ous and evergreen species partition resources both temporally and spat ially, thereby reducing interspecies competition.