Detection, isolation and characterization of a root‐exuded compound, methyl 3‐(4‐hydroxyphenyl) propionate, responsible for biological nitrification inhibition by sorghum (Sorghum bicolor)

• Nitrification results in poor nitrogen (N) recovery and negative environmental impacts in most agricultural systems. Some plant species release secondary metabolites from their roots that inhibit nitrification, a phenomenon known as biological nitrification inhibition (BNI). Here, we attempt to characterize BNI in sorghum (Sorghum bicolor). • In solution culture, the effect of N nutrition and plant age was studied on BNI activity from roots. A bioluminescence assay using recombinant Nitrosomonas europaea was employed to determine the inhibitory effect of root exudates. One major active constituent was isolated by activity-guided HPLC fractionations. The structure was analysed using NMR and mass spectrometry. Properties and the 70% inhibitory concentration (IC70) of this compound were determined by in vitro assay. • Sorghum had significant BNI capacity, releasing 20 allylthiourea units (ATU) g−1 root DW d−1. Release of BNI compounds increased with growth stage and concentration of supply. -grown plants released several-fold higher BNI compounds than -grown plants. The active constituent was identified as methyl 3-(4-hydroxyphenyl) propionate. • BNI compound release from roots is a physiologically active process, stimulated by the presence of . Methyl 3-(4-hydroxyphenyl) propionate is the first compound purified from the root exudates of any species; this is an important step towards better understanding BNI in sorghum.