Evaluation of a crop rotation with biological inhibition potential to avoid N2O emissions in comparison with synthetic nitrification inhibition.

Agriculture has increased the release of reactive nitrogen to the environment due to crops' low nitrogen-use efficiency (NUE) after the application of nitrogen-fertilisers. Practices like the use of stabilized-fertilisers with nitrification inhibitors such as DMPP (3,4-dimethylpyrazole phosphate) have been adopted to reduce nitrogen losses. Otherwise, cover crops can be used in crop-rotation-strategies to reduce soil nitrogen pollution and benefit the following culture. Sorghum (Sorghum bicolor) could be a good candidate as it is drought tolerant and its culture can reduce nitrogen losses derived from nitrification because it exudates biological nitrification inhibitors (BNIs). This work aimed to evaluate the effect of fallow-wheat and sorghum cover crop-wheat rotations on N2O emissions and the grain yield of winter wheat crop. In addition, the suitability of DMPP addition was also analyzed. The use of sorghum as a cover crop might not be a suitable option to mitigate nitrogen losses in the subsequent crop. Although sorghum-wheat rotation was able to reduce 22% the abundance of amoA, it presented an increment of 77% in cumulative N2O emissions compared to fallow-wheat rotation, which was probably related to a greater abundance of heterotrophic-denitrification genes. On the other hand, the application of DMPP avoided the growth of ammonia-oxidizing bacteria and maintained the N2O emissions at the levels of unfertilized-soils in both rotations. As a conclusion, the use of DMPP would be recommendable regardless of the rotation since it maintains NH4+ in the soil for longer and mitigates the impact of the crop residues on nitrogen soil dynamics.

Biological nitrification inhibitor-trait enhances nitrogen uptake by suppressing nitrifier activity and improves ammonium assimilation in two elite wheat varieties.

Synthetic nitrification inhibitors (SNI) and biological nitrification inhibitors (BNI) are promising tools to limit nitrogen (N) pollution derived from agriculture. Modern wheat cultivars lack sufficient capacity to exude BNIs, but, fortunately, the chromosome region (Lr#n-SA) controlling BNI production in Leymus racemosus, a wild relative of wheat, was introduced into two elite wheat cultivars, ROELFS and MUNAL. Using BNI-isogenic-lines could become a cost-effective, farmer-friendly, and globally scalable technology that incentivizes more sustainable and environmentally friendly agronomic practices. We studied how BNI-trait improves N-uptake, and N-use, both with ammonium and nitrate fertilization, analysing representative indicators of soil nitrification inhibition, and plant metabolism. Synthesizing BNI molecules did not mean a metabolic cost since Control and BNI-isogenic-lines from ROELFS and MUNAL presented similar agronomic performance and plant development. In the soil, ROELFS-BNI and MUNAL-BNI plants decreased ammonia-oxidizing bacteria (AOB) abundance by 60% and 45% respectively, delaying ammonium oxidation without reducing the total abundance of bacteria or archaea. Interestingly, BNI-trait presented a synergistic effect with SNIs since made it also possible to decrease the AOA abundance. ROELFS-BNI and MUNAL-BNI plants showed a reduced leaf nitrate reductase (NR) activity as a consequence of lower soil NO 3 - formation and a higher amino acid content compared to BNI-trait lacking lines, indicating that the transfer of Lr#-SA was able to induce a higher capacity to assimilate ammonium. Moreover, the impact of the BNI-trait in wheat cultivars was also noticeable for nitrate fertilization, with improved N absorption, and therefore, reducing soil nitrate content.

Enlisting wild grass genes to combat nitrification in wheat farming: A nature-based solution.

Active nitrifiers and rapid nitrification are major contributing factors to nitrogen losses in global wheat production. Suppressing nitrifier activity is an effective strategy to limit N losses from agriculture. Production and release of nitrification inhibitors from plant roots is termed "biological nitrification inhibition" (BNI). Here, we report the discovery of a chromosome region that controls BNI production in "wheat grass" Leymus racemosus (Lam.) Tzvelev, located on the short arm of the "Lr#3Nsb" (Lr#n), which can be transferred to wheat as T3BL.3NsbS (denoted Lr#n-SA), where 3BS arm of chromosome 3B of wheat was replaced by 3NsbS of L. racemosus We successfully introduced T3BL.3NsbS into the wheat cultivar "Chinese Spring" (CS-Lr#n-SA, referred to as "BNI-CS"), which resulted in the doubling of its BNI capacity. T3BL.3NsbS from BNI-CS was then transferred to several elite high-yielding hexaploid wheat cultivars, leading to near doubling of BNI production in "BNI-MUNAL" and "BNI-ROELFS." Laboratory incubation studies with root-zone soil from field-grown BNI-MUNAL confirmed BNI trait expression, evident from suppression of soil nitrifier activity, reduced nitrification potential, and N2O emissions. Changes in N metabolism included reductions in both leaf nitrate, nitrate reductase activity, and enhanced glutamine synthetase activity, indicating a shift toward ammonium nutrition. Nitrogen uptake from soil organic matter mineralization improved under low N conditions. Biomass production, grain yields, and N uptake were significantly higher in BNI-MUNAL across N treatments. Grain protein levels and breadmaking attributes were not negatively impacted. Wide use of BNI functions in wheat breeding may combat nitrification in high N input-intensive farming but also can improve adaptation to low N input marginal areas.

Mechanism of action of nitrification inhibitors based on dimethylpyrazole: A matter of chelation.

In agriculture, the applied nitrogen (N) can be lost in the environment in different forms because of microbial transformations. It is of special concern the nitrate (NO3-) leaching and the nitrous oxide (N2O) emissions, due to their negative environmental impacts. Nitrification inhibitors (NIs) based on dimethylpyrazole (DMP) are applied worldwide in order to reduce N losses. These compounds delay ammonium (NH4+) oxidation by inhibiting ammonia-oxidizing bacteria (AOB) growth. However, their mechanism of action has not been demonstrated, which represent an important lack of knowledge to use them correctly. In this work, through chemical and biological analysis, we unveil the mechanism of action of the commonly applied 3,4-dimethyl-1H-pyrazole dihydrogen phosphate (DMPP) and the new DMP-based NI, 2-(3,4-dimethyl-1H-pyrazol-1-yl)-succinic acid (DMPSA). Our results show that DMP and DMPSA form complexes with copper (Cu2+) cations, an indispensable cofactor in the nitrification pathway. Three coordination compounds namely [Cu(DMP)4Cl2] (CuDMP1), [Cu(DMP)4SO4]n (CuDMP2) and [Cu(DMPSA)2]·H2O (CuDMPSA) have been synthesized and chemical and structurally characterized. The CuDMPSA complex is more stable than those containing DMP ligands; however, both NIs show the same nitrification inhibition efficiency in soils with different Cu contents, suggesting that the active specie in both cases is DMP. Our soil experiment reveals that the usual application dose is enough to inhibit nitrification within the range of Cu and Zn contents present in agricultural soils, although their effects vary depending on the content of these elements. As a result of AOB inhibition by these NIs, N2O-reducing bacteria seem to be beneficed in Cu-limited soils due to a reduction in the competence. This opens up the possibility to induce N2O reduction to N2 through Cu fertilization. On the other hand, when fertilizing with micronutrients such as Cu and Zn, the use of NIs could be beneficial to counteract the increase of nitrification derived from their application.