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

Abstract

Background and aims: 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. Methods: 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. Results: 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. Conclusions: 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.