Effects of lanthanum(III) and EDTA on the growth and competition of Microcystis aeruginosa and Scenedesmus quadricauda

Rare earth elements (REEs) are widely used to increase crop production in China. However, little attention has been paid to their impacts on aquatic ecology. Batch cultivation was used here to study the effects of lanthanum (La) and EDTA on the growth and competition of the cyanobacteriurn Microcystis aeruginosa and the green alga Scenedesmus quadricauda. When EDTA was present at a very low concentration (0.269 mu mol L(-1)), low lanthanum concentrations (<= 7.2 mu mol L(-1)) had little stimulative effect oil the growth of M. aeruginosa and S. quadricauda, whereas a high lanthanum concentration (72 mu mol L(-1)) had significant inhibitory effect oil both of them. The results of cultivation experiments suggested that the inhibitory effect on M. aeruginosa was higher than that oil S. quadricauda and S. quadricauda could become dominant in mixed cultures. When lanthanum was not added to the culture medium, high EDTA concentrations (> 13.4 mu mol L(-1)) had a great inhibitory effect on the growth of M. aeruginosa but little effect on the growth of S. quadricauda, which could become dominant in the mixed cultures. Lanthanum and EDTA had complex effects on the growth and competition of M. aeruginosa and S. quadricauda. EDTA did not change the stimulation of low lanthanum concentrations on both, but at intermediated concentrations (2.69-13.4 mu mol L(-1)) it could greatly alleviate lanthanum inhibition on M. aeruginosa; thus, M. aeruginosa would dominate S. quadricauda in these mixed cultures. Lanthanum at low concentration (7.2 mu mol L(-1)) could also alleviate the inhibition of high EDTA oil M. aeruginosa, but did not alter the outcome of the competition. (C) 2008 Elsevier GmbH. All rights reserved.