Inhibitory effect of Cinnamomum camphora and Ginkgo biloba leaves seawater extract on Prorocentrum donghaiense and analysis of its active constituent
Harmful algal bloom(HAB)is an increasingly serious marine environmental problem in many coastal areas around the world.Prorocentrum donghaiense is the main dominant species of HAB in the East China Sea.Plant allelopathy has the advantages of high efficiency,selectivity,no secondary pollution,and little impact on ecology,so it has become a hot spot of HAB control.Cinnamomum camphora and Ginkgo biloba have been proven to have inhibitory effects on some freshwater algae and red tide algae,but their inhibitory components and mechanisms have not been thoroughly studied.In this study,the defoliations of C.camphora and G.biloba were used to study the allelopathic inhibition effects of their room temperature seawater extracts on the bloom-forming species P.donghaiense.The constituents in C.camphora seawater extracts were analyzed by headspace-solid phase micro extraction combined with gas chromatography/mass spectrometry.The components in seawater extract of G.biloba leaves were analyzed by ultra performance liquid chromatography tandem quadrupole time of flight mass spectrometry.The inhibitory components were screened out.The results showed that the 96 h-EC50 of C.camphora and G.biloba seawater extracts against the growth of P.donghaiense were 1.23 g·L-1 and 1.22 g·L-1,respectively.The algal inhibition effect of C.camphora extract was slower than that of G.biloba,but its inhibitory effect on P.donghaiense was more lasting.The cell growth inhibition rate of P.donghaiense treated by C.camphora extracts with a concentration higher than 3.0 g·L-1 was higher than 71.00%at 96 h.C.camphora extract had little effect on the swimming of algae in the early stage of the experiment(within 48 h),but after 72 h of treatment,it could cause the algae in high concentration experimental groups to burst and die quickly.The terpenes of sea water extract from C.camphora leaves were analyzed,and linalool,nerolidol,spathulenol,1,8-cineole,beta-santalene and bergamotol were identified.The algal inhibition effect of G.biloba extract was faster,and the algal cell swimming ability was inhibited after 24 h.After 96 h,the growth inhibition rate of 2.0 g·L-1 G.biloba extract reached 84.61%.The flavonoid compounds in the seawater extract of G.biloba were detected,and catechin,rutin and quercetin were identified.These three compounds have been confirmed to have algal inhibition effect.It was found that nerolidol had an inhibitory effect on P.donghaiense.At 48 h,nerolidol of different concentration gradients had significant inhibitory effects on P.donghaiense(P<0.05).After 96 h treatment,the inhibition rates of nerolidol at 1.0,2.0,4.0,8.0 mg·L-1 were 40.34%,68.72%,99.55%and 99.18%,respectively.The 96 h-EC50 of nerolidol against the growth of P.donghaiense was 1.25 mg·L-1.In addition,nerolidol could rapidly cause P.donghaiense to lose swimming ability when treated for 24 h,but the duration was shorter at low concentrations.After 72 h,the inhibitory effect decreased.The combination of C.camphora and G.biloba leaves is expected to develop a compound algal suppressant with rapid effect and lasting action time,which can play a better preventive role in the early outbreak of red tide in offshore cage culture sea area.Nerolidol is a potential active ingredient for algal inhibition.Studies on the allelopathic mechanism of nerolidol on harmful algae and the synergistic effect of nerolidol with plant leaves or other algal inhibitory compounds can be carried out in the later stage,to provide theoretical basis for the development of plant-derived compound algal inhibitory agent.