Cost-Benefit Relationships in Deciduous and Evergreen Leaves of Tropical Dry Forest Species

Abstract

Evidence from previous studies relates the significance of evergreeness and deciduousness to differences in leaf drought resistance and nutrient-use characteristics. Considering possible differences in leaf construction costs and lifespans in both plant types, I hypothesized that they should have contrasting strategies underlying their nitrogen-use efficiency (NUE) and water-use efficiency (WUE). Thus, leaves of six deciduous and four evergreen species were analysed to compare their construction and maintenance costs, maximum CO2 assimilation capacity (Amax) and potential (instantaneous) NUE and WUE. Leaf construction and maintenance costs were always higher in evergreen than in deciduous species. The largest Amax were recorded in some deciduous species. However, another deciduous species had Amax comparable to evergreen leaves. Therefore, a clear-cut difference between deciduous and evergreen leaves was not detected. However, NUE and WUE related to construction cost differences in the two plant groups. Indeed, NUE and WUE were largest in deciduous plants. Notwithstanding, overall carbon return per unit invested nitrogen may be increased in evergreens because leaves are photosynthetically active for longer periods. In fact, increases in the ratio between investment (construction cost) to potential payback (Amax) increase leaf life-spans (payback interval). Nevertheless, in tropical dry forests deciduous species are dominant and evergreen species are scarce. Carbon diversion to non-photosynthetic tissue (deep roots) and highest leaf cost may offset competitive capability of evergreen species. Key-words: Carbon assimilation, construction costs, deciduous, evergreen, maintenance cost, nitrogen-use efficiency, tropical dry forest, water-use efficiency