Synergistic Effect In Algal Suppression By Four Typical Aquatic Macrophytes

Allelopathy of aquatic macrophytes is of significance on composition ofcommunities in freshwater ecosystems and ecological rehabilitation in eutrophic lakes. Inorder to investigate a new method of mitigating the deleterious effect of harmful algalblooms (HABs), the inhibition of the four aquatic macrophytes Ranunculus sceleratus Linn,Alternanthera philoxeroides, Trapa quadrispinosa Roxb and Nymphoides peltatum onMicrocystis aeruginosa and Chlorella pyrenoidosa was studied under controlledlaboratory conditions. The main results are indicated as following:1) The extracts of4aquatic macrophytes exhibited significant inhibitory effects onM. aeruginosa and C. pyrenoidosa. The maximum algal inhibitory rate was over70%. Furthermore, the inhibition of four individual extracts on M. aeruginosaand C. pyrenoidosa was concentration-dependent. That is, as the initialconcentration of four individual extracts in the cultures increased, thepercentage inhibition increased correspondingly. However, the extracts from T.quadrispinosa and N. peltatum can stimulate the growth of M. aeruginosa at a lowconcentration of2g/L. Also, the result shows that C. pyrenoidosa can bestimulated by the extracts from R. sceleratu, A. philoxeroides and N. peltatum atlower concentrations (2-10g/L).2) The inhibitory effects on M. aeruginosa and C. pyrenoidosa are more significantduring the lag phase than those during the exponential phase by the4individualextracts.3) The inhibition of the4individual extracts on M. aeruginosa and C. pyrenoidosa was species-specific. Allelopathic inhibitory effects on M. aeruginosa by the4individual extracts were indicated in a descending order: R. sceleratus＞A.philoxeroides＞N. peltatum＞T. quadrispinosa. For C. pyrenoidosa, allelopathiceffects were also shown in a declining order: T. quadrispinosa＞R. sceleratus＞A.philoxeroides＞N. peltatum.4）Based on stronger individual algal inhibition effects by the3extracts, R.sceleratus, A. philoxeroides and T. quadrispinosa, the effects of binary extracts atvarious ratios (1:9,3:7,5:5,7:3,9:1) were studied．The results showed thatmore significant algal inhibition was observed at the ratio of1:9,9:1and5:5.5）The effects of the extracts from different parts of R. sceleratus on M. aeruginosaand C. pyrenoidosa were further investigated. The results indicated that theeffects of the various tissue extracts on M. aeruginosa were shown in adescending order: root＞stem＞leaf and for C. pyrenoidosa in a decliningorder: root＞leaf＞stem.6）Extracts from R. sceleratus strongly suppressed algal chlorophylls. The resultsshowed that extracts from R. sceleratus slightly affected POD and CAT of M.aeruginosa at the initial stage. However, the extracts at higher concentrations(10g/L,20g/L,30g/L, and40g/L) significantly inhibited the activities ofalgal enzymes.