Photoinhibition of Photosynthesis in Plants Growing in Natural Tropical Forest Gaps. A Chlorophyll Fluorescence Study

Photoinhibition of photosynthesis was monitored by means of chlorophyll a fluorescence in leaves of plants growing in 60–80 m 2 light gaps in a moist tropical lowland forest located on Barro Colorado Island in central Panama. In these forest gaps, photon flux density was low (less than 100 μmol photons m −2 s −1 ) during most of the day, but increased on clear days to 1.7‐1.8 mmol photons m −2 s −1 for 1–2 h during midday. Nine species representing different taxa and life‐forms were examined. Leaves of all species exhibited substantial photoinhibition in situ during high light exposure, as manifested by a decrease in the ratio of variable to maximum fluorescence emission, F V /F M . Recovery (reversion of fluorescence quenching) took place in the shade following high light exposure. The major part of recovery occurred in a fast phase within about 1 h after the high light period. A slow phase of recovery proceeded for another 4–5 h until sunset. After 30–60 min of recovery in the shade, calculated rates of PSII electron transport remained significantly (5–15%) reduced in comparison to rates obtained prior to high light exposure; after about 2 h of recovery, inhibition was negligible. All species responded to the high light periods and following shade periods in a very similar manner. It is concluded that photoinhibition and recovery exhibited by these gap leaves reflect a dynamic regulatory mechanism of thermal energy dissipation that allows plants of different life‐forms to cope with periods of high light in tropical forest gaps.