The Photo-physiological Inhibited Mechanism On Heterosigma Akashiwo By Four Typical Macroalgae

With the elevated level of Hamful algal blooms(HABs) frequency and their concomitant damages, HABs draw the scientists’ attention globally. How to mitigate the red tide effectively has became a hot research subject. Macroalgae, eco-friendly and abundant resource in marine areas, are important contributors to coastal primary productivity, can be used as good biological control material to reduce HABs. While, most of the previous researches were focused on the apparent growth of HABs, photosynthetic mechanism of the seaweed inhibiting red tide algae is not well established. This experiment was co-cultured Heterosigma akashiwo(H. akashiwo) with four macroalgae Ulva fasciata(U. fasciata), Gracilaria lemaneiformis(G. lemaneiformis), Gracilaria tenuistipitata(G. tenuistipitata) and Gracilaria chouae(G. chouae). With the photosynthesis as the main line, the controlled mechanism on H. akashiwo by four macroalgae acquired by the following parameters, such as cell growth, JIP-test, Chlorophyll synthesis and electron transport chain. The main results of the research were as follows:1) U. fasciata can significantly reduce the growth rate of H. akashiwo. When co-cultured for 48 h, the growth rate of H. akashiwo was inhibited as high as 58.4% by 3 g/L dried U. fasciata. After 96 h co-culture, 2.5 g/L fresh U. fasciata exerted 98.8% inhibition rate on H. akashiwo, even higher than that by 5 g/L fresh U. fasciata at the same period, which showed that the inhibitory rate was not enhanced by the fresh algae reaching a certain concentration threshold. The result showed that the low concentration of U. fasciata stimulated H. akashiwo cell growth, while inhibited by the high biomass of macroalga. The maximum photosynthetic oxygen evolution rate(Pmax) in H. akashiwo were significantly decreased, while the dark respiration rate(Rd) wereincreased. U. fasciata showed the effect of damaging the H. akashiwo’s oxygen-evolving complex(OEC), blocking its electron transport chain, and inhibiting its PSⅡ.Those impacts were dose-dependent.2) G.lemaneiformis yielded significantly negative effect on the growth of H. akashiwo. In 48 co-culture treatment, 3 g/L dried G. lemaneiformis inhibited H. akashiwo by 69.9%. For 96 h co-cultured H. akashiwo, inhibition rate by 5g/L fresh G. lemaneiformis was 98.8%. Pmax in H. akashiwo was significantly decreased, while Rd were increased. Except 72 h and 96 h treatments, fresh G. lemaneiformis displayed a highly negative effect on fraction of OEC in H. akashiwo, while the other chlorophyll fluorescence parameters fluctuated same as that in the U. fasciata.3) G. tenuistipitata also negatively affected the growth of H. akashiwo. H. akashiwo was inhibited as high as 60.7% by 3 g/L dried G. tenuistipitata after 48 h co-culture. For 5 g/L fresh G. tenuistipitata, the inhibition rate was 55.6% in 96 h co-cultured H. akashiwo. Pmax in microalga decreased significantly, while Rd increased. Dried G. tenuistipitata showed a significantly negative effect on TRo/RC in H. akashiwo, while the other chlorophyll fluorescence parameters was same as the U. fasciata. The results suggested that dried G. tenuistipitata damaged the PSⅡactivity in H. akashiwo via non-QA-reducing.4) Fresh G. chouae can significantly lowed the growth rate of H. akashiwo. For 96 h co-culture with 5 g/L fresh G. chouae, inhibition rate on H. akashiwo was 44.5%. Except dried G. chouae played a highly negative effect on ETo/RC in H. akashiwo, the other chlorophyll fluorescence parameters showed the same pattern as that in the U. fasciata.Briefly, during the initial co-cultured stage, dried macroalgae showed more stronger inhibition effect on H. akashiwo than fresh algae. For the later stage, the other three macroalge displayed the same patter as those in the initial period, except for the U. fasciata, whose dried algal sample inhibition effect was better than the fresh one. Generally, for fresh macroalgae inhibiting effect, the order is as follows: U. fasciata > G. lemaneiformis > G. tenuistipitata > G. chouae; while for the dried one, the inhibiting effect display the following pattern: G. lemaneiformis > G. tenuistipitata > U. fasciata. During the experiments, fresh macroalgae occured as natural deposition, dry algae and sterilized glass brads sank to the bottom after sealed in silk screen. We also added nutrient after each sampling. Thus it can rule out the competition of shading or nutrient in the function of the inhibition on microalgae. Then, we speculated that it was possible the four macroalgae could release active allelochemicals, which can significantly inhibit the growth rate and oxygen evolution rate of H. akashiwo. Macroalgae may also effectively inhibit PSⅡactivity in H. akashiwo by lowering PSⅡdonor side OEC and hindering the PSⅡreceptor side electrons transfer from QA- QB.