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Photosynthesis and photosynthetic electron transport in the soft coral Sarcophyton spp

Vipawee Dummee^a,b, Suhailar Sma-air^a, Suksiri Chooklin^a, Thanongsak Chanmethakul^c, Raymond J. Ritchie^a,b,*

 
ABSTRACT:     Blue-diode Pulse Amplitude Fluorometry (PAM) and rapid light curves, fitted using the Waiting-in-Line equation, were used to measure photosynthetic electron transport rate (ETR) of the common soft coral Sarcophyton spp (Alcyoniidae, Cnidaria). Optimum irradiance (Eopt) of newly-collected material was 353?28.9 ?mol quanta m?2 s ?1 (?18% sunlight, 400?700 nm), ? optimum irradiance (E1/2?ETR) ?82.0 ?mol quanta m?2 s ?1 with substantial photoinhibition at higher irradiances. Maximum ETR (ETRmax) = 25.1?1.28 ?mol e? m?2 s ?1 (surface area basis) or 86.8?4.44 ?mol e? g ?1 Chl a s ?1 (Chl a basis). Due to strong midday inhibition total daily photosynthesis would be greater on cloudy days, during the overcast wet season and high tides. Open aquarium-grown material had Eopt ?300 ?mol quanta m?2 s ?1 ; ETRmax ?21 ?mol e? m?2 s ?1 or ?50 ?mol e? g ?1 Chl a s ?1 . Chl a was ?300 (field material) vs. ?450 (aquaculture aquarium) mg m?2 but with no change in Chl c2/a ratio (0.521?0.0181). Based on light/dark O2 electrode methods in aquaria Gross Photosynthesis (Pg ) = 21.9?6.85 ?mol O2 g ?1 Chl a s ?1 , Pnet = 15.1?6.38 ?mol O2 g ?1 Chl a s ?1 ; respiration ?6.81?2.23 ?mol O2 g ?1 Chl a s ?1 ; P/R ratio = 3.72?1.86 at an irradiance 192?20.3 ?mol quanta m?2 s ?1 . The culturable dinoflagellate zooxanthellae material might not necessarily be representative of the resident zooxanthellae population. Their PAM characteristics were similar to the soft coral (Eopt ?219 ?mol quanta m?2 s ?1 , ETRmax ?138 ?mol e? g ?1 Chl a s ?1 ), but the Chl c2/a ratio (?0.16) was very different.

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* Corresponding author, E-mail: raymond.r@phuket.psu.ac.th

Received 31 May 2022, Accepted 12 Dec 2022