Unraveling DMPSA nitrification inhibitor impact on soil bacterial consortia under different tillage systems

Nitrogen (N) applied with fertilizers is not efficiently used in agriculture. In the soil, this N is transformed into different compounds by means of several biological processes. As a result, there is a negative economic and environmental impact due to water contamination, via nitrate (NO3-) leaching, and greenhouse gasses emission, via nitrous oxide (N2O). To reverse this situation, nitrification inhibitors (NI) such as dicyandiamide (DCD), nytrapirin and 3,4-dimethylpyrazole phosphate (DMPP) are widely applied to agricultural soils in order to delay ammonium (NH4+) transformation. A new NI, 3,4-dimethylpyrazole-succinic acid (DMPSA), has been recently developed with the aim of deploying a specific action on ammonium-oxidizing bacteria (AOB). However, previous studies have demonstrated that DMPSA application increases nosZl gene abundance. Thus, non-target populations involved in N-cycle are also affected by its application. For better understanding the effects of DMPSA addition, this NI was applied with ammonium sulfate (AS) fertilizer in a winter wheat crop soil under Humid Mediterranean conditions, in two different soil tillage managements (conventional tillage, CT; and notillage, NT). Soil samples were then analyzed by 16S rRNA amplicon sequencing. DMPSA application induced a decrease in bacterial alpha-diversity under the NT management, which showed higher water-filled pore space (WFPS) than the CT management. This suggests that water content played a key role in DMPSA effects. Even at the phyla level, the abundances of several non-target organisms, either involved or not in the N-cycle, were affected by DMPSA application. Within them, the biggest changes were found in Cyanobacteria (+ 48%) phylum (considered promising bio-agents for sustainable agriculture), which may have also triggered the increase of Bacteroidetes (+ 20%) and the decrease of certain phytopathogens. This decrease of phytopathogens may have also been helped by the great increase observed after DMPSA application in the genus Vermamoeba vermiformis, a protist known to control/regulate several soil-borne pathogens. Altogether, the results showed that DMPSA may lead to a reduction of the environmental impacts derived not only from the loss of reactive N, but also from the maintenance of a safer microbial community for plant health. However, further studies would be necessary to analyze the persistence and the consequences of all these effects in the long-term.