Cost-benefit relationships in sclerophyllous leaves of the ‘Bana’ vegetation in the Amazon region

Abstract

This study estimated the construction const (CC) and maintenance cost (MC) of leaf tissue on the basis of dry mass (CC_Mass, MC_Mass) and leaf area (CC_Area, MC_Area), as well as the maximum leaf gas exchange capacity, so as to examine leaf cost:benefit relationship in six dominant species of the ‘Bana’ vegetation. Minimum and maximum CC_Mass averaged 1.71 ± 0.03 and 1.78 ± 0.03 g glucose g⁻¹. The CC_Mass showed a statistically significant positive correlation with crude fibre, and tended to decline as leaves were larger. Thus, smaller leaves tended to be built out of a more expensive material than that found in species bearing larger leaves. The average CC_Area of the ‘Bana’ species was 376 ± 15 g glucose m⁻². A robust correlation was found between CC_Area with leaf dry mass to leaf area ratio, as well as with leaf thickness, but not with leaf density. MC_Mass (g glucose g⁻¹ day⁻¹) and MC_Area (g glucose m⁻² day⁻¹⁾ were positively correlated. Maximum and minimum MC_Mass increased significantly with protein and lipid content, respectively. Maximum carbon assimilation (A _max) was positively correlated with CC_Area. All the species operated at high stomatal conductance (g _s) and C _i/C _a which suggested low short-term water use efficiency. Potential nitrogen use efficiency (PNUE = A _max/N) averaged 35.4 ± 1.8 mmol CO₂ mol⁻¹ N. As the sclerophylly index (g crude fibre g⁻¹ protein) increased, the ratio of CC_Area to A _max increased significantly. This result suggests a trade-off between investments in an expensive resistant sclerophyllous leaf which should maximize carbon gain in the long term.