Allelopathic influence of Myriophyllum spicatum on the photosynthetic efficiency of Microcystis aeruginosa

The allelopathic influence of Myriophyllum spicatum on chlorophyll content and chlorophyll fluorescence parameters of Microcystis aeruginosa was studied in coexistence condition.Chlorophyll fluorescence parameters included qN(non-photochemical quenching),Y Ⅱ(effective quantum yield),Fv/Fm(maximum quantum yield),F′v/F′m(effective quantum yield of photosystem Ⅱ photochemistry) and ETR(electron transport rate).During the three days under coexistence condition,chlorophyll content and chlorophyll fluorescence parameters of M.aeruginosa were affected by M.spicatum and presented different sensitivities.Chlorophyll content of M.aeruginosa was significantly inhibited by 20.80% on the second day at 10.0 g/L of M.spicatum(P0.05).However,chlorophyll fluorescence parameters of M.aeruginosa decreased earlier and rapider than chlorophyll content.On the first day,qN and Y Ⅱ of M.aeruginosa were significantly inhibited by 15.59% and 13.00% at 5.0 g/L of M.spicatum(P0.05),and Fv/Fm and F′v/F′m were declined by 15.87% and 12.07% at 10.0 g/L(P0.05),respectively.On the third day,ETR and three parameters based on ETR were affected at all levels of M.spicatum(P0.05).The inhibition effects on the photosynthetic activity of M.aeruginosa might be considered as one of the target sites of M.spicatum and chlorophyll fluorescence parameters were more sensitive parameters than chlorophyll content,especially qN.