A cost-benefit analysis of leaves of eight Australian savanna tree speciesof differing leaf life-span

Cost-benefit analyses of foliar construction and maintenance costs and of c arbon assimilation of leaves of differing life-span were conducted using tw o evergreen, three semi-deciduous, and three deciduous tree species of sava nnas of north Australia. Rates of radiant-energy-saturated CO2 assimilation (P-max) and dark respiration were measured and leaves were analysed for to tal nitrogen, fat, and ash concentrations, and for heat of combustion. Spec ific leaf area, and leaf N and ash contents were significantly lower in lon ger-lived leaves (evergreen) than shorter-lived leaves (deciduous) species. Leaves of evergreen species also had significantly higher heat of combusti on and lower crude fat content than leaves of deciduous species. On a leaf area basis, P-max was highest in leaves of evergreen species, but on a leaf dry mass basis it was highest in leaves of deciduous species. P-max and to tal Kjeldahl N content were linearly correlated across all eight species, a nd foliar N content was higher in leaves of deciduous than evergreen specie s. Leaf construction cost was significantly higher and maintenance costs we re lower for leaves of evergreen than deciduous species. Maintenance and co nstruction costs were linearly related to each other across all species. Le aves of evergreen species had a higher cost-benefit ratio compared to leave s of deciduous species but with longer lived leaves, the payback interval w as longer in evergreen than deciduous species. These results support the hy potheses that longer lived leaves are more expensive to construct than shor t-lived leaves, and that a higher investment of N into short-lived leaves o ccurs which supports a higher P-max over a shorter payback interval.