Does subjecting plants to water stress enhance biological nitrification inhibition potential of rice?

Abstract Background and aims: Biological nitrification inhibition (BNI) is a trait that could improve nitrogen-use efficiency of a crop. We studied varietal differences in BNI potential of rice at the vegetative phase when plants were subjected to water stress. Methods We obtained water-soluble root exudates (RE) and water-extracts of crushed roots (RT) from two week-old seedlings of five rice varieties grown continuously under adequate water or under water stress and assessed their ability to suppress the activity of Nitrosomonas europaea and the growth of lettuce seedlings. We also investigated how growing rice under continuously saturated (TC) and unsaturated (TU) soil moisture conditions affected potential nitrification rate (PNR) and the community structure of ammonia-oxidizing archaea and bacteria (AOA and AOB, respectively) in the rhizosphere compared with the bulk soil. Results We observed that only RT at ≥ 0.50 mg ml− 1suppressed the activity of N. europaea with significant (p < 0.05) differences among rice varieties. Subjecting rice varieties PI312777 and PI338046 to water stress significantly (p < 0.05) increased BNI of RT. Inhibition of lettuce root growth by RT was strongly correlated with its BNI (r = 0.83, p < 0.05). As revealed in T-RFLP profiles, varietal effects on AOA and AOB varied with moisture management. AOB were more responsive to soil moisture conditions than AOA. Conclusions The rice varieties studied produced compounds that could inhibit ammonia oxidizers, but the degree of BNI differed based on moisture stress faced by the crop. Lineages of rice varieties with known allelopathic potential would be promising candidates in a search for BNI potential.