Photosynthetic Responses of Tropical Forest Plants to Contrasting Light Environments

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Abstract

Across the complex matrix of microsites that compose tropical forests, light availability varies more dramatically than any other single plant resource. On a sunny day, instantaneous measurements of photosynthetically active radiation range over 3 orders of magnitude, from less than 10 µmol m-2 s-1 in closed-canopy understory of mature forests to well over 1000 µmol m-2 s-1 in exposed microsites of gaps and large clearings, or at the top of the forest canopy (Chazdon & Fetcher, 1984b; Figure 1.1). Among the environmental factors that influence plant growth and survival in tropical forests, light availability is likely to be the resource most frequently limiting growth, survival, and reproduction (Chazdon, 1988; Fetcher, Oberbauer & Chazdon, 1994). Photosynthetic utilization of light is therefore a major component of the regeneration responses of forest species within the larger context of forest dynamics and succession.