Sub-lethal glyphosate disrupts photosynthetic efficiency and leaf morphology in fruit-producing plants, red raspberry (Rubus idaeus) and highbush cranberry (Viburnum edule)

Abstract

Glyphosate-based herbicides are widely used in Canadian silviculture to control competing vegetation, particularly broadleaf plants, and non-target, understory plants are often exposed to sub-lethal doses. Understory plants such as red raspberry (Rubus idaeus) and highbush cranberry (Viburnum edule) play many integral ecological roles, which may be altered by glyphosate.To determine the effects of sub-lethal glyphosate on raspberry and cranberry plant growth and health, experimental plots were established in the central interior of British Columbia, Canada, using a nested design. Plots were treated with 0.3% VisionMax™ after which, leaf dimensions were quantified and leaf formation assessed, and chlorophyll fluorescence, total flavonoid and rutin concentrations were measured on a weekly basis.Treated cranberry plants produced new leaves that were smaller overall, while treated raspberry plants had narrower leaves. There were a higher proportion of abnormal leaves in treated plants. Photosynthetic performance was hampered in all treated plants; cranberry plants appeared to recover more quickly however. Flavonoid concentration was largely unaffected although rutin concentration increased in treated cranberry leaves.The two species responded differently to sublethal glyphosate in their morphology and physiology, and that likely altered overall growth and health. We discuss the ecological consequences of such alterations on forage availability and habitat quality.