XVI International Botanical Congess

Photosynthetic characteristics were investigated in the geographically isolated and restricted mangrove species, P. rhizophoreae. Gas exchange measurements were made on two to seven year old hydroponically grown plants maintained in 10%, 50% and 100% seawater. CO2 exchange in the 50% and 100% seawater treatments was reduced by 10% and 26% respectively, compared to the 10% seawater treatment. CO2 response curves indicated that carboxylation efficiency was greater in 10% than in 50% seawater, while stomatal limitation increased from 11% to 16% as salinity increased from 10% to 50% seawater. Carbon losses via photorespiration (31% and 41%) and CO2 compensation point (67ul l-1 and 81ul l-1) were greater in 50% than in the 10% seawater treatment. Maximal CO2 exchange occurred at 30 oC with no differences among the salinity treatments. The results indicate that P. rhizophoreae exhibits many gas exchange characteristics previously reported for other mangroves.