Effects Of Inorganic Carbon Alkalinity And Coexisting Green Algae On The Interaction Between Pyrogallol And Microcystis Aeruginosa

The increasing frequency and magnitude of harmful cyanobacterial blooms has been driven by eutrophication.This is a threat to the structure and function of aquatic ecosystems.Cyanobacteria,however,are more sensitive to allelopathic inhibition of submerged macrophytes than eukaryotic algae,which is quite valuable for biological management of eutrophic water bodies.The present study aimed to explore the influencing factors of the application of allelopathic substances derived from submerged plants in the control practice of cyanobacterial bloom.Pyrogallol,one typical allelochemical of submerged macrophyte Myriophyllum spicatum,was selected to investigate the effects of inorganic carbon alkalinity,and co-existing green algae on pyrogallol toxicity to one dominant cyanobacteria species,Microcystis aeruginosa.At the same time,a solid-phase extraction-silanization-gas chromatography method was established for the dynamic determination of pyrogallol concentrations in the process of cyanobacterial inhibition.The main results were as follows:(1)A solid-phase extraction-silanization-gas chromatography method was established for the determination of pyrogallol in water,by improving the silanization method,and comparing the effects of different eluting solvents,elution volumes and pH values of water samples before enrichment on the extraction efficiency.The method can also be used for simultaneous quantification of nonanoic acid.The characteristic peak of nonanoic acid and pyrogallol was identified according to the retention time of the standards.Their characteristic peak area was used for quantitative analysis.It was shown that the simultaneous and rapid detection of nonanoic acid and pyrogallol in water could be accomplished,with a recovery rate above 80%,by using Oasis HLB solid phase extraction column(10 mg,1 cc)for extraction,1 mL of acetone for subsequent elution and equal proportions of acetone and BSTFA for silanization.The developed method can be applied to the studies on dynamic behaviors of allelochemicals belonging to fatty acids and phenolic acids,and provides technical support for the research on allelopathic mechanisms of aquatic plants.(2)Inorganic carbon alkalinity not only affects inorganic carbon availability of cyanobacteria,but also affects the environmental behavior of various chemical components in the water.The effects of varying inorganic carbon alkalinity on pyrogallol toxicity to alkalinity-adapted and un-adapted M.aeruginosa were investigated separately in the study.It showed that the inhibitory effects of pyrogallol at 5.0 mg/L on M.aeruginosa,pre-adapted to specific alkalinity,increased with the increase of inorganic carbon alkalinity from 0.09 mmol/L to 1.51 mmol/L after 3-day exposure.The inhibitory effects of pyrogallol at 5.0 mg/L on un-adapted M.aeruginosa increased with the increase of inorganic carbon alkalinity from 0.05 mmol/L to 6.04 mmol/L after 12-day exposure.Acceleration of the autooxidation process of pyrogallol by higher inorganic carbon alkalinity,resulting in the production of more quinones and oxygen radicals,was deduced as the reason why higher inorganic carbon alkalinity enhanced pyrogallol toxicity.Therefore,the inorganic carbon alkalinity level of applied water must be considered when using pyrogallol to control cyanobacteria.(3)In order to simulate the coexistence of various algae in natural water and to discuss whether the coexisting algae has an impact on pyrogallol toxicity to target cyanobacteria,the green algae with high economic value,Haematococcus pluvialis was selected to co-culture with M.aeruginosa.The effects of pyrogallol on both species in the mixed co-culture and the pure culture systems were compared.The results showed that the inhibitory effects of pyrogallol on M.aeruginosa were significantly stronger than that on H.pluvialis in both culture systems(p<0.05).The inhibition rate of pyrogallol on the growth of M.aeruginosa in the co-culture system was lower than that in the pure system,and the increase extent of extracellular microcystin contents was significantly lower than that in the pure culture(p<0.05).However,the inhibition rate of pyrogallol on the growth of H.pluvialis was significantly enhanced(p<0.05),and cell quota of intracellular astaxanthin was much higher in the co-culture systems compared to that in the pure culture.These preliminary results indicated the inhibitory effects of pyrogallol on M.aeruginosa was reduced while that on H.pluvialis was enhanced when they were co-existing,and it can be deduced that the co-existence of phytoplankton species could affect the inhibitory effects of allelochemicals on target algae or cyanobacteria.The biotic and abiotic environment factors of target organisms should be fully considered to further study allelopathic inhibition on phytoplankton,and it would help us to reveal the ecological mechanisms of this process and ecological value of allelopathy as well as allelochemicals.