Leaf traits of canopy trees on a precipitation gradient in Panama: Integrating plant physiological ecology and ecosystem science.

摘要

There is increasing awareness in ecology of the importance of species effects on processes at the ecosystem scale. This dissertation uses a comparative approach involving many species along a precipitation gradient (1800--3500 mm/yr) in lowland Panama to understand how species traits vary among different plant communities, and how these traits feed back into ecosystem processes such as decomposition and soil nutrient availability. As precipitation increases from south to north across the Isthmus of Panama, there is a gradual change in canopy leaf traits from short-lived leaves with high photosynthetic rates in seasonally dry forest, to relatively long-lived leaves with lower photosynthetic rates and increased allocation to structural defense in wet forest. Increases in leaf litter lignin:N also accompany increases in precipitation, indicating a decrease in potential decomposability of leaf litter in wetter sites. Leaf litter lignin:N was negatively correlated with soil N mineralization rates, and positively correlated with total soil N pools indicating that slowly decomposing litter reduces mineralization, but conserves N in the soil organic matter matrix. Leaf litter lignin:N was the strongest litter quality predictor of decomposition at the one site where decomposition was studied. Decomposition was positively related to specific leaf area, leaf N concentration and photosynthetic rate per unit mass suggesting that these traits may be useful predictors of the effects of species on ecosystem processes. Photosynthetic rate per unit area and stomatal conductance were positively related to leaf specific hydraulic conductivity and negatively related to branch wood density indicating that leaf traits controlling gas exchange correlate with processes at the branch and whole plant levels of organization. Overall this dissertation provides evidence that many plant traits are correlated along a minimal number of axes, and that these traits can be used to predict the movement of matter and energy between plants and their environments.