Drought effects on photosynthetics of the mangrove, Avicennia germinans, under contrasting salinities
1999
Sobrado, M.A.
Drought effects on leaf photosynthesis of A. germinans growing under two contrasting salinities were studied in a Venezuelan fringe mangrove. During both wet and dry seasons, severe chronic-photoinhibition at predawn was not observed but strong down regulation occurred at midday during both seasons. Carbon assimilation rates (A, micromol CO2 m-(2) s-(1)) declined during the dry season from 11.9 +-1.8 to 7.0 +- 1.5 and from 9.6 +- 2.0 to 4.7 +- 2.5 in plants from low and highsalinity sites, respectively. Changes in carbon assimilation per unit of chlorophyll (A/Chl, mmol CO2 mol-(1) Chl) were from 31.6 +- 4.7 to 20.5 +- 4.3 and from 21.9 +- 4.7 to 15.2 +- 8.2 in the low and high salinity plants, respectively. Therefore, neither changes in Chl nor seasonal differences in photoprotective down regulation could account fully for the decrease in leaf photosynthesis during drought. A reduction in CO2 diffusion due to lowered stomatal conductance was not large enough to explain such a dramatic effect of drought on leaf photosynthesis. Stomatal response could be mitigated by the capability of A. germinans for osmotic adjustment under high salinity and/or drought. However, this intracellular salt accumulation may reduce carbon assimilation capacity further by decreasing the metabolism of leaf cells, increasing dark respiration and/or photorespiration.
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