Glyphosate influence on phytoplankton community structure in Lake Erie

In this study we investigated the effect of the phosphonate herbicide glyphosate (N-(phosphonomethyl) glycine) on the phytoplankton community structure in Like Erie using lake water incubations, laboratory growth experiments and phylogenetic analysis of phosphonate metabolism genes. In microcosms, addition of glyphosate to Sandusky Bay water resulted in a significant increase in phytoplankton abundance, specifically causing an increase in the abundance of Planktothrix spp. In microcosms using Maumee Bay water, glyphosate did not stimulate phytoplankton growth but caused a decrease in Microcystis spp. abundance. The difference in the ability of Planktothrix spp. and Microcystis spp. to grow in the presence of glyphosate was confirmed in laboratory growth experiments. Further, an examination of the molecular pathways involved in phosphonate metabolism demonstrated that heterotrophic bacteria may be critical in allowing this proliferation. The results indicate that glyphosate has both positive and negative influences on phytoplankton community structure, serving as a nutrient source to microbes able to tolerate the herbicidal effects of the compound while killing those less tolerant. Moreover, this work highlights that in natural environments microorganisms function as communities, and the metabolic abilities of individual species are often less important than the collective ability of the community. (C) 2011 International Association for Great lakes Research. Published by Elsevier B.V. All rights reserved.