PARENT SESSION
Oral Session #24: Forests: Carbon allocation, carbon budgets. Presiding: C. Reid.
Tuesday, August 7, 2001. 8:00 AM to 11:15 AM. Hall of Ideas F.

Photosynthetic capacity and associated leaf traits along a precipitation gradient in lowland tropical forest.

SANTIAGO, LOUIS¹, ¹

ABSTRACT- Patterns of leaf photosynthetic characteristics along precipitation gradients are of interest because they are thought to reflect specific evolutionary adaptations to a gradient of environmental regimes. We measured photosynthetic capacity with an oxygen electrode and associated leaf traits of canopy trees along a rainfall gradient (1800-3600 mm/year) in Panamanian lowland tropical forest. Maximum photosynthetic rate, leaf N concentration, specific leaf area (SLA), leaf thickness and leaf toughness were measured during the wet season when all species had leaves. Photosynthetic rate per unit leaf area did not vary significantly with precipitation, however, photosynthetic rate per unit leaf mass decreased with increasing rainfall. Variation in mass-based photosynthesis can be partially explained by increasing leaf thickness and decreasing SLA with increasing rainfall. Leaf toughness and C/N ratios also increased with increasing rainfall suggesting that patterns of leaf characteristics along this gradient may influence decomposition and nutrient availability following senescence. The pattern of maximum photosynthetic rate increasing with leaf N and SLA is in accordance with previous studies. Increasing photosynthetic capacity and associated traits with decreasing rainfall indicates that species in drier forest exhibit leaf traits that allow them to utilize higher light availability, whereas species in wetter forest tend to exhibit leaf traits associated with lower light availability.

KEY WORDS: photosynthesis, rainfall gradient, tropical forest, Panama