Physiological and biochemical responses of Microcystis aeruginosa to glyphosate and its Roundup® formulation.

Glyphosate may have dual effect on bloom algae as a phosphorus source or pesticide. The physiological and biochemical responses of Microcystis aeruginosa (M. aeruginosa) to glyphosate and its formulation in the common herbicide, Roundup(®), were compared. The result suggested that both the cell numbers and Chl-a content of M. aeruginosa increased when the glyphosate concentration increased from 0.01 to 5mg P L(-1). However, Roundup(®) showed low-dose (below 1mg P L(-1)) stimulation and high-dose (above 1mg P L(-1)) inhibition on M. aeruginosa cell density and Chl-a content (hormesis effect). Phosphate was more available than glyphosate or Roundup(®), and Roundup(®) was more toxic than glyphosate itself at 3mg P L(-1). Analysis of the maximum yield of PSII indicated that glyphosate stimulated the photosynthesis process while Roundup(®) inhibited the photosynthesis of M. aeruginosa. The photosynthesis process was enhanced on the 21st day compared with that on the 14th day in all P mediums. The extracellular alkaline phosphatase activity (APA) decreased with the increasing glyphosate or Roundup(®) concentration. The change pattern of APA was similar in both the glyphosate and Roundup(®) mediums.