Morphological and photosynthetic studies on Gracilarian species from Trat Province, eastern Thailand

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Morphological and photosynthetic characteristics of the three Thai species of Gracilaria, G. changii, G. firma and G. salicornia distributed in the same habitat at Cho Bay, Trat Province, eastern Thailand were studied. The three species can be identified morphologically, however, some specimens have intermediate morphologies among them. G. firma has terminal branches without or with some furcations and blunt apices, first-order of branches always constricted at the bases; G. changii has many branches, inflated at the middle and tapering toward apices, all branches abruptly constricted at the bases; G. salicornia has cylindrical to compressed branches with regular or irregular arrangement of branches, constricted or continuous and intermediate species has branches inflated, tapering to apices, with and without constriction at bases. To elucidate the species status of Gracilaria species, we examined their photosynthetic and respiratory responses to irradiance and temperature by Oxygen Analyzer Series 3600. Net photosynthetic rate in species of Gracilaria from Trat Province was dependent on temperature. It increased with an increase in temperature from 25-35℃, while the rate decreased at 40℃. Photosynthetic responses were similar for all species when plants were exposed from 30 to 35℃. The P_<max> was significantly highest at 35℃ (0.39mg O_2cm^<-2>h^<-1>) for intermediate species, while the lowest was at 40℃ in G. firma (0.09mg O_2cm^<-2>h^<-1>). The photosynthetic rate responses to high irradiance and temperature by intermediate species are indicative of either adaptation to environmental variation or an outcome of hybridization between the three species.
東京大学の論文
2006-04-28

Morphological and photosynthetic studies on Gracilarian species from Trat Province, eastern Thailand

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