Identification of several wheat landraces with biological nitrification inhibition capacity

Background and aims Nitrification is the first step in several pathways that lead to losses of nitrogen from agricultural systems. Biological nitrification inhibition (BNI) refers to the ability of some plant species to release chemicals from their roots that inhibit microbial ammonia oxidation thereby decreasing nitrification rates. BNI has been found in the wheat relative Leymus racemosus but not in Triticum aestivum. The aim of this work was to assess a number of landraces of Triticum aestivum for BNI ability. Methods Samples of root exudates and root tissue extracts, collected from hydroponically grown plants, were tested for their impact on nitrification rates when inoculated with pure cultures of two ammonia oxidising bacteria, Nitrosomonas europaea and Nitrosospira multiformis. Pot experiments were then conducted to confirm the results. Results The vast majority of the landraces tested caused some level of inhibition. However, of the 96 wheat landraces tested, 26 produced root exudates which caused a statistically significant reduction in nitrification rates of the two ammonia oxidising bacteria. Root exudates from four of the BNI positive landraces were shown to significantly inhibit nitrification rates in a sandy loam soil. Conclusions This is the first evidence of significant levels of BNI in Triticum aestivum. The discovery of landraces with BNI ability raises the potential for breeding this trait into modern, elite wheat cultivars.