Fate of glyphosate in lakes with varying trophic levels and its modification by root exudates of submerged macrophytes.

Accelerated eutrophication in lakes reduces the number of submerged macrophytes and alters the residues of glyphosate and its degradation products. However, the effects of submerged macrophytes on the fate of glyphosate remain unclear. We investigated eight lakes with varying trophic levels along the middle and lower reaches of the Yangtze River in China, of which five lakes contained either glyphosate or aminomethylphosphate (AMPA). Glyphosate and AMPA residues were significantly positively correlated with the trophic levels of lakes (P < 0.01). In lakes, glyphosate is degraded through the AMPA and sarcosine pathways. Eight shared glyphosate-degrading enzymes and genes were observed in different lake sediments, corresponding to 44 degrading microorganisms. Glyphosate concentrations in sediments were significantly higher in lakes with lower abundances of soxA (sarcosine oxidase) and soxB (sarcosine oxidase) (P < 0.05). In the presence of submerged macrophytes, oxalic and malonic acids secreted by the roots of submerged macrophytes increased the abundance of glyphosate-degrading microorganisms containing soxA or soxB (P < 0.05). These results revealed that a decrease in the number of submerged macrophytes in eutrophic lakes may inhibit glyphosate degradation via the sarcosine pathway, leading to a decrease in glyphosate degradation and an increase in glyphosate residues. soxA and soxB promote glyphosate degradation via the sarcosine pathway. The abundances of soxA and soxB in sediments play a decisive role in determining the residual amount of glyphosate in lakes at different trophic levels. Submerged macrophytes increase the abundance of glyphosate-degrading microorganisms containing soxA or soxB. The results presented here indicate that the decline of submerged macrophytes is the primary cause of the increased glyphosate residues in eutrophic lakes. This study reveals the primary causes of increased glyphosate residues in eutrophic lakes and helps devise strategies for minimizing the accumulation of glyphosate in lakes. [Display omitted] • Residues of glyphosate + AMPA increased with lake eutrophication (P < 0.01). • Eight common glyphosate-degrading genes were detected in different lake sediments. • Glyphosate degradation was significantly affected by soxA and soxB (P < 0.05). • Plant root exudates could regulate microorganisms containing soxA and soxB. • Decline of submerged macrophytes leads to residual glyphosate in eutrophic lakes. [ABSTRACT FROM AUTHOR]