Plant acquisition and metabolism of the synthetic nitrification inhibitor dicyandiamide and naturally-occurring guanidine from agricultural soils

There is increasing interest and use of nitrification inhibitors (NI) in agroecosystems, yet little is known of their fate in planta. Residues of the organic, N-rich NI, dicyandiamide (DCD), have been found in milk products following commercial application to pasture. We investigated whether plant acquisition and metabolism of DCD were consistent with plant-mediated transmission from soil to agricultural food products. Uptake rates, translocation to the shoot, degradation of the label within wheat tissue and availability within two soils of DCD and the structurally similar naturally occurring N-rich molecule, guanidine, were measured using 14C labelling. Under sterile conditions, over 2 h wheat took up (34 and 14 μmol g−1 root DW h−1 at 1 mM: DCD and guanidine, respectively), translocated (7–15 and 19–22 %) and metabolised (0.4 and 0.9 % of uptake) DCD- and guanidine-14C. Both molecules were also acquired from soil by wheat despite concurrent soil sorption and microbial uptake. Both DCD and guanidine can be acquired and metabolised by graminaceous plants. Although probably not a significant route of N acquisition, plant uptake provides a direct route of DCD entry into the food chain.