The Photo-physiological Controlling Mechanism On Three Typical Red Tide Microalgae By The Macroalga Ulva Fasciata

Using macroalgae as a novel, low cost and environmental friendly material tocontrol HABs, is widely recognized by the international society. While presently,most of researches are focusing on the apparent effects by macroalgae algicidalactivity against the growth of red tide algae. Still, little is known about the mechanism,especially the most basic photo-physiological mechanism of algicidal activity bymacroalga. In this study, we use chlorophyll a fluorescence technology to elucidatethe photo-physiological controlling mechanism of algicidal activity on three red tidemicroalgae by macroalga Ulva fasciata. The primary results were as follows:1) Ulva fasciata can significantly inhibit the growth and photosynthetic oxygenevolution rate of Scrippsiella trochoidea. At the same time, the quantum yield forelectron transport of PSⅡ(φEo), probability that a trapped exciton moves an electroninto the electron transport chain beyond QA-(ψo) and the fraction of OEC of S.trochoidea were significantly decreased by U. fasciata. Nevertheless, the variablefluorescence intensity at the K-step(Wk), the relative variable fluorescence intensityat the J-step(Vj) and the rate of QAreduction (Mo) were significantly higher when S.trochoidea was exposed to U. fasciata.2) The photosynthetic oxygen evolution rate of Skeletonema costatum wassignificantly inhibitted by U. fasciata. The chlorophyll a fluorescence parameters of S.costatum, when exposed to U. fasciata, have the same variation trend as describeabove. Compare with the control group, the φEo, ψo, φPo and Fraction of OEC oftreatment group were significantly lower. While the Wk, Vj, Mo were significantlyhigher when S. costatum was exposed to U. fasciata.3) U. fasciata showed significantly inhibitting effect on the growth ofProrocentrum micans. We did not measure photosynthetic rate in this study, so thereis no photosynthetic oxygen evolution rate data. But the chlorophyll a fluorescenceparameters of P. micans exposed to U. fasciata have the same variation trend as S. trochoidea and S. costatum. φEo, ψo and φPo decreased when P. micans was exposedto U. fasciata. Cells of P. micans exposed to U. fasciata had higher Wk, Vj and Movalue. But the Fraction of OEC of treated P. micans is higher, which is different withthe treated S. trochoidea and S. costatum.In conclusion, our results showed that U. fasciata can significantly inhibit thegrowth of S. trochoidea, S. costatum and P. micans. We use chlorophyll afluorescence technology to analyze the algicidal activity on PS Ⅱof three red tidemicroalgae by macroalga U. fasciata. The results indicate the mechanism of algicidalactivity on S. trochoidea, S. costatum and P. micans by U. fasciata are disruption atboth donor site (oxygen evolving complex) and acceptor site (block the electrontransport from QA-to QB) of PS Ⅱ, andinactivation of reactive center of PS Ⅱ.