Influence of Nitrogen and Humidity on Rhizome Bud Growth and Glyphosate Translocation in Quackgrass (Agropyron repens)

When buds on the rhizome of quackgrass [ Agropyron repens (L.) Beauv.] were released from apical dominance either by increasing the nitrogen supply to the parent shoot (from 5.25 to 210 ppm) or by raising the humidity around the rhizome (from 55 to 100%), the growth response of the buds was closely correlated with their uptake of foliar-applied 14 C-labeled glyphosate [ N -(phosphonomethyl] glycine]. The 14 C level in the buds, expressed on a dry-weight basis, was greatest in the youngest, most rapidly growing bud at the apical node and decreased in successively older buds along the rhizome. A similar gradient was shown by the 14 C content of the associated rhizome nodes. The high-humidity treatment also increased the total amount of 14 C that was translocated into the rhizome, whereas increasing the nitrogen supply, while promoting 14 C uptake by the buds, markedly reduced the amount in the rhizome nodes and in other parts of the plant. This nitrogen-induced reduction in translocation was associated with a reduction of about 30% in uptake of the herbicide by the treated leaves.