Phosphate (PO43-) fertilization is a common practice in agricultural fields also targets for glyphosate application. Due to their chemical similarities, PO43- and glyphosate compete for soil adsorbing sites, with PO43- fertilization increasing glyphosate bioavailability in the soil solution. After PO43- fertilization, its concentration will be elevated in the soil solution and both PO43- and glyphosate will be readily available for runoff into aquatic ecosystems. In this context, man-made riparian buffer strips (RBS) at the interface of agricultural lands and waterways can be used as a green technology to mitigate water contamination. The plants used in RBS form a barrier to agricultural wastes that can limit runoff, and the ability of these plants to take up these compounds through their roots plays an important role in RBS efficacy. However, the implications of PO43- for glyphosate uptake by roots are not yet clearly demonstrated. Here, we addressed this problem by hydroponically cultivating willow plants in nutrient solutions amended with glyphosate and different concentrations of PO43-, assuring full availability of both chemicals to the roots. Using a phosphate carrier inhibitor (phosphonophormic acid-PFA), we found that part of the glyphosate uptake is mediated by PO43- transporters. We observed, however, that PO43- increased glyphosate uptake by roots, an effect that was related to increased root cell membrane stability. Our results indicate that PO43- has an important role in glyphosate physiological effects. Under agricultural conditions, PO43- fertilization can amplify glyphosate efficiency by increasing its uptake by the roots of undesired plants. On the other hand, since simultaneous phosphate and glyphosate runoffs are common, non-target species found near agricultural fields can be affected.
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