DCPIPC-Hill reaction activity was mainly used to measure the electron transfer capability from water to DCPIPC in photosynthetic system II (PSII) (Bährs and Steinberg 2012). The combined analyses of Figs. 1 and 3 showed that, even though the algae growth was greatly inhibited (IR% reached 83.33 %) after 5-days culturing of mixed allelochemicals and M. aeruginosa, the DCPIPC-Hill reaction activity of all the treatment groups had not been affected by allelochemicals (P > 0.05). Thus, it could be included that allelochemicals released from P. stratiotes root exudates had no effect on the electron transfer of PS II in M. aeruginosa. According to the linear regression analysis, there was a positive correlation between PC/APC level and algae density (r 2 = 0.643, P