HighlightsPhosphate increased glyphosate uptake and decreased its toxicity in willows PO 4 3-concentrations ≥ 200 mg l -1 doubled glyphosate uptake by willow roots PO 4 3-concentrations ≥ 200 mg l -1 increased antioxidant system activity PO 4 3-maintained photosynthesis rates by inducing reactive oxygen species scavenging 3 Abstract Phosphate (PO 4 3-) has been shown to increase glyphosate uptake by willow, a plant species known for its phytoremediation potential. However, it remains unclear if this stimulation of glyphosate uptake can result in an elevated glyphosate toxicity to plants (which could prevent the use of willows in glyphosate-remediation programs). Consequently, we studied the effects of PO 4 3-on glyphosate uptake and toxicity in a fast growing willow cultivar (Salix miyabeana SX64). Plants were grown in hydroponic solution with a combination of glyphosate (0, 0.001, 0.065 and 1 mg l -1 ) and PO 4 3-(0, 200 and 400 mg l -1 ). We demonstrated that PO 4 3-fertilization greatly increased glyphosate uptake by roots and its translocation to leaves, which resulted in increased shikimate concentration in leaves. In addition to its deleterious effects in photosynthesis, glyphosate induced oxidative stress through hydrogen peroxide accumulation.Although it has increased glyphosate accumulation, PO 4 3-fertilization attenuated the herbicide's deleterious effects by increasing the activity of antioxidant systems and alleviating glyphosateinduced oxidative stress. Our results indicate that in addition to the glyphosate uptake, PO 4 3-is involved in glyphosate toxicity in willow by preventing glyphosate induced oxidative stress.

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The use of glyphosate-based herbicides (GBHs) in industrial agriculture has intensified in the past decades, causing a growing concern about the occurrence and spatial distribution of glyphosate and its principal metabolite, aminomethylphosphonic acid (AMPA), in the environment. In 2014, glyphosate and AMPA content was measured in 45 soils from the St. Lawrence Lowlands (Quebec, Canada) before seeding and at harvest in soybean field crops using various weed management practices with or without GBH applications. At the same time, a recent history of agricultural practices and soil conditions was compiled for the sampled sites. The results of the study show that 91% of the samples contained detectable amount of either glyphosate or AMPA, with maximum values of 0.47 mg·kg−1 and 1.16 mg·kg−1 for glyphosate and AMPA, respectively. Surprisingly, detectable amounts of AMPA were measured in fields not treated with GBHs in 2014, whereas traces of both glyphosate and AMPA were detected in organic field crops, highlighting the potential spreading and/or persistence of both compounds in the environment. Glyphosate content was significantly higher in clay soils rich in exchangeable cations, such as Mg2+, K+ and Ca2+, which can contribute to the retention of glyphosate in soil via complexation processes.

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