Trade-offs and constraints in carbon allocation along Savanna to Rain Forest gradients: Predictions and processes at ecosystem level

BUCCI, S.J., SCHOLZ F.G., GOLDSTEIN G., MEINZER F.C., FRANCO A., MIRALLES WILHELM F.

Kumming China

Simposio; ATBC Conference; 2006

Linking physiological and morphological traits of individual species with the function of ecosystems is an important current theme in ecology and is critical for predicting the impact associated with changes in biodiversity and climate. The conflictive allocation of resources tends to constrain the number of possible combinations of functional traits in a particular individual and among species, leading to functional convergence across a broad range of species. Because the combination of species characteristics are site specific, the constraints in species and life history traits should be reflected in ecosystems structure and function. Average specific leaf area (SLA), wood density, midday leaf water potentials (YL), diurnal variations in YL and specific and leaf specific hydraulic conductivity were studied in several sites along a tree density gradient in Central Brazil from open savannas to savanna woodlands to tropical rain forests. We have found, for example, that higher wood density stands (e.g. open savannas) tended to exhibited lower SLA, more negative YL and lower hydraulic conductivities compared to lower wood density sites such as savanna woodlands and tropical forests. Wood density reflects the pattern of carbon allocation in woody plant stems, which depends on the proportion of wood volume occupied by cell wall material and water- and air-filled spaces. Ecosystem properties result in part from the collective characteristics of all individual organisms in a particular site. How these individual traits scale to impact ecosystem level processes is currently unclear. We are hypothesizing that weighted average wood density decreases with improving soil nutrient availability. Sites with low weighted average wood density will have higher net primary productivity, higher canopy transpiration and trees with higher photosynthetic capacity compared to sites with high weighted average wood density. Sites with high weighted average wood density and therefore leaves with low SLA that tend to decompose slowly are characterized by slow nutrient return and relatively low soil nutrient availability.