Effect of methyl 3-4-hydroxyphenyl propionate, a Sorghum root exudate, on N dynamic, potential nitrification activity and abundance of ammonia-oxidizing bacteria and archaea

It has been reported that root exudates of Sorghum bicolor can inhibit nitrification in a bioassay using Nitrosomonas, and methyl 3-(4-hydroxyphenyl) propionate (MHPP) was identified as one of the nitrification inhibiting compounds. Therefore, we have investigated the effects of this compound on nitrogen dynamic, potential nitrification activity and on soil microorganisms. We conducted soil incubation experiments using synthetic MHPP to evaluate its effect on changes in inorganic soil nitrogen pools, on nitrification activity and on abundance of ammonia-oxidizing bacteria and archaea. Addition of MHPP at two concentrations equivalent to 70 and 350 mu g C g(-1) soil was compared to glucose as a carbon source and to the commercially available nitrification inhibitor dicyandiamide (DCD). Soil amended with the high dose of MHPP and with DCD showed reduced nitrate content and low nitrification activity after 3 and 7 days of incubation. This was mirrored by a 70 % reduction in potential nitrification activity compared to a nitrogen-only control. None of the incubation treatments affected non-target microbial counts as estimated by 16S rRNA gene copy numbers, however, the high dose of MHPP significantly reduced the abundance of ammonia-oxidizing bacteria and archaea. These findings suggest that MHPP is capable of suppressing nitrification in soil, possibly by reducing the population size and activity of ammonia-oxidizing microorganisms.