The Effects Of PUAs On The Growth, Photosynthesis And Pigments Accumulation Of Three Species Of Phytoplankton

Diatoms are important primary production of marine ecosystem and have been considered as the major source of food and energy for copepods. Therefore these organisms are fundamental in the process of material cycle and energy flow of marine food chain. However, some diatom could produce organic polyunsaturated aldehydes(PUAs) once cell wounding. Previous studies have showed that these organic toxins could inhibit the reproduction of copepods, as well as the development of larva, and thus reduce grazing pressure. But the allelopathic effects of PUAs on phytoplankton are lacking. We conducted experiments to explore the effects of PUAs on the growth, photosynthesis and pigments composition of phytopalnktons. Prorocentrum donghaiense, Chaetoceros didymus and Prymnesium parvum were exposed to 2E,4E-Heptadienal(HEP), 2E,4E-Octadienal(OCT) and 2E,4E-decadienal(DEC) with different concentrations,respectively, and the growth, photosynthesis were measured. The concentrations of pigments in Prorocentrum donghaiense, Chaetoceros decipiens and Prymnesium parvum exposing to different concentrations of DEC were tested as well.We selected HEP, OCT and DEC with different concentration to study the effects of these toxic chemicals on the growth and photosynthesis of Prorocentrum donghaiense, Chaetoceros didymus and Prymnesium parvum. The results showed that these effects had species and concentration of specificity. The molecular weight of HEP was the smallest in these three selected PUAs, however its toxic effects on algae were lowest. HEP could inhibit the growth and photosynthesis of P. donghaiense with high concentration of 10 mg·L-1, but it had no any effects on the other two species. OCT clearly decreased the cell abundance and photosynthesis of P.donghaiense and C. didymus when its concentration was up to 5 mg·L-1. The growth and photosynthesis of phytoplankton were depressed significantly when exposed to DEC with lower concentration. Thus the longer carbon chain of PUA was, the stronger toxic effect it had. These three PUAs could inhibit the growth and photosynthesis of P. donghaiense. OCT and DEC had negative influence on C. didymus. However the response of P. parvum to DEC was only at high concentration. Therefore, in three selected algae, P. donghaiense was the most sensitive species.The toxic effect of DEC was most remarkable in these three types of PUAs. We selected different concentrations of DEC to study the effect of PUAs on the concentration and composition of pigments in P. donghaiense, C. decipiens and P. parvum with HPLCmethod.When DEC concentration was up to 3 mg·L-1, the concentrain of all pigments of P.donghaiense decreased significantly. DEC at 5 mg·L-1led to the decreased concentration of pigments in C. decipiens and P. parvum, but three days later there was Zeaxanthin or Diatoxanthin in these two species. Thus DEC could clearly influence the distribution of pigments in phytoplankton.The effects PUAs on phytoplankton are dependly on the species, concentration and exposure time. PUAs inhibit photosynthesis of phytoplankton through influencing the types and composition of pigments, and then have negative effect on their growth. Therefore diatom-derived PUAs have capability to suppress the growth of competitive phytoplankton during algal bloom, thereby supporting the biomass accumulation of diatom and regulating the structure and function of food chain.