| Summary: | 碩士 === 國立彰化師範大學 === 生物學系 === 91 === The photosynthetic light responses of Thalassia hemprichii at three sites in the Hengchun Peninsula (southern Taiwan) were measured in situ with submersible pulse amplitude modulated (Diving-PAM) fluorometer. T. hemprichii from Wanlitung showed the highest photosynthetic light response, followed by Dakwan and then Nanwan. Point measurements under 55ºC were also conducted on field-collected seagrass samples to measure the heat-induced Fv/Fm change. T. hemprichii at Nanwan (usually exposed to the air) had the highest heat tolerance followed by Wanlitung (tidal pool) and then Dakwan. On the other hand, the RLCs (rapid light curves) of Halophila decipiens were measured in situ at Wanlitung. In the field, the ETRmax value was 4.2 µmol electrons m-2s-1 and was reached at actinic light intensity of 160 PPFD (in µmol photons m-2s-1). The effects of salinity and temperature on the photosynthetic light response of Ha. decipiens and its mean ETRmax ranged from 2.31—3.26 µmol electrons m-2s-1 and 0.70—3.76 µmol electrons m-2s-1, respectively. The optima temperature of Ha. decipiens ranged from 27—37°C and suggest that it is a tropical species.
The RLCs of five seagrass (Enhalus acoroides、Thalassia hemprichii、Cymodocea rotundata、Halodule uninervis、Halophila ovalis) were determined in situ in a small embayment at Maribago, Mactan Island, Philippines. All RLCs reached ETRmax values at light intensity between 150-250 PPFD. T. hemprichii had the highest photosynthetic light response and was widely distribution in this embayment, while Ha. ovalis had the lowest photosynthetic light response and confined itself to the ‘middle’ and ‘lower’ intertidals. Specimens of C. rotundata and T. hemprichii from the ‘upper’ intertidal and Hd. uninervis from the ‘lower’ intertidal fully recovered in the LC-RECOVERY (light curve-recovery) function of Diving-PAM fluorometer.
Photosynthetic light responses of 22 species seaweeds were measured in situ around the seashores of Hengchun Peninsula, southern Taiwan. Chlorophytes species had the highest ETRmax value (13.7 μmol electrons m-2s-1) followed by Phaeophytes species (7.0 μmol electrons m-2s-1) and then Rhodophytes species (4.3 μmol electrons m-2s-1). According to the morphological form of seaweeds, the photosynthetic light response ranked as following: siphonous group (17.8 μmol electrons m-2s-1)> sheet group (12.9 μmol electrons m-2s-1)> thick leathery group (6.6 μmol electrons m-2s-1) and jointed calcareous group (6.6 μmol electrons m-2s-1)>crustose group (4.2 μmol electrons m-2s-1). Codium (siphonous form) had the highest photosynthetic light response, and the ETRmax value was 17.8 µmol photons m-2s-1. In the experiments of the effects on seaweed desiccation and rewetness, we found that Ulva lactuca from the ‘upper’ intertidal showed better desiccation-tolerant than Colpomenia sinuosa from the ‘lower’ intertidal. Even the relative water content of U. lactuca reduced to 20%, its ETRmax value could recover to 93.3% comparing with the sample of 100% relative water content.
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