A Sunfleck Over a Sapling in Barro Colorado Island

Recorded during the dry season on Jan 26th 2017 at the Smithsonian Tropical Research Institute (STRI) in Barro Colorado Island, Panama. A short duration sunfleck passes over a sapling of Nectandra cissiflora (Lauraceae).

Plants growing in the forest understory habitats can be exposed to fast microclimatic changes. Although light is essential for plants, sudden exposure to high light can be detrimental to shade adapted leaves. Sunflecks can be destructive for the photosystem II (PSII), a component of the photosynthetic apparatus powerful enough to split water to release oxygen into the atmosphere. Plants must adapt rapidly to high-light environments in order to minimize damaging effects of intense flow of electrons into photosynthetic reaction centers. Here in this short observation over the course of a few minutes a shaded sapling is exposed to a spike of high photon flux.

The aquatic ancestor of land plants have evolved photosynthetic light harvesting complexes bearing a reaction center. One of the challenges of being a land plant is to find a solution to endure sudden influx of photons. Many plants rearrange the composition of the light harvesting antennae proteins to minimize damage. This rearrangement can be likened to a lightening rod draining and dissipating excess photons in the form of heat. Plant molecular biologists call these “lightening rods” as non-photochemical quenching centers.

Although many early successional tropical species can have a persistent seed bank, many don’t. Seeds of most tropical trees cannot stay viable for long durations in soil. Instead of a seed bank the regeneration and replenishment of tropical forests is dependent on seedling bank. Long-term ecological monitoring studies have shown that seedlings and saplings can wait for many years without growing until a disturbance leads to an opening in the canopy. The sapling Nectandra cissiflora (Lauraceae) observed here is similarly waiting for such a window of opportunity to reach the canopy. Evolving a flexible light harvesting complex could provide a survival advantage enabling exploitation of occasional high light situations.

Understanding individual leaf properties is important to extrapolate processes that govern forests such as photosynthetic rates, transpiration and carbon assimilation. Scientific “Big Leaf” models that treat the entire forest as a single leaf have to take sun exposed and shaded leaves into account in order to make accurate calculations.

 

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