Photosynthesis and growth of red and green morphotypes of Kappaphycus alvarezii (Rhodophyta) from the Philippines

The effect of photosynthetic available radiation (PAR) levels, light qualit y, ultraviolet (UV) radiation, and temperature on photosynthesis, growth, a nd chlorophyll fluorescence was evaluated in red and green morphotypes of t he rhodophyte Kappaphycus alvarezii (Doty) Doty under controlled conditions . Chlorophyll a and phycoerythrin (PE) levels were similar in the red and g reen morphotypes cultured under the same conditions, but phycocyanin (PC) a nd allophycocyanin (APC) levels were 2-fold greater in the green than in th e red morphotype. Pigment characterization indicated that the overexpressio n of PC and APC masked the red pigmentation in the green morphotype, Maximu m photosynthesis and photosynthetic efficiency were similar between the two morphotypes assayed at a wide temperature range, which was reflected in th e similar growth rates observed in outdoor culture systems. In the green mo rphotype, photosynthetic efficiency increased 2-fold relative to the red mo rphotype when assayed with red light (lambda > 600 nm), indicating that pho tosynthetic characteristics are modified as a result of pigment variation i n these morphotypes. Such increase in photosynthetic efficiency in the gree n morphotype, however, did not result in greater growth rates when cultured under white light. Short exposure to high levels of solar radiation (UV-A + UV-B + PAR), and filtered solar radiation (UV-A; PAR or PAR) decreased ef fective quantum yield (DeltaF/F-m') in both morphotypes. The reduction of D eltaF/F-m' values in the red and green morphotypes was accounted for by hig h levels of PAR and not by the UV-A + UV-B + PAR and UV-A + PAR treatments. Photoinhibition caused by UV-A, UV-B, or PAR was completely reversed withi n 30 h after incubations. Recovery rates from photoinhibition, however, wer e significantly reduced in the green morphotype when incubated with UV-B ra diation. The results here suggest that the overexpression of pigments do no t necessarily increase photosynthesis and growth in these morphotypes.