Open Access
Biological and synthetic approaches to inhibiting nitrification in non-tilled Mediterranean soils
(SpringerOpen, 2021) Bozal-Leorri, Adrián; Corrochano Monsalve, Mario; Arregui Odériz, Luis Miguel; Aparicio Tejo, Pedro María; González Murua, Carmen; Agronomía, Biotecnología y Alimentación; Agronomia, Bioteknologia eta Elikadura; Ciencias; Zientziak
Background: The increasing demand for food production has led to a tenfold increase in nitrogen (N) fertilizer use since the Green Revolution. Nowadays, agricultural soils have been turned into high-nitrifying environments that increase N pollution. To decrease N losses, synthetic nitrification inhibitors (SNIs) such as 3,4-dimethylpyrazole phosphate (DMPP) have been developed. However, SNIs are not widely adopted by farmers due to their biologically limited stability and soil mobility. On the other hand, allelopathic substances from root exudates from crops such as sorghum are known for their activity as biological nitrification inhibitors (BNIs). These substances are released directly into the rhizosphere. Nevertheless, BNI exudation could be modified or even suppressed if crop development is affected. In this work, we compare the performance of biological (sorghum crop) and synthetic (DMPP) nitrification inhibitors in field conditions. Results: Sorghum crop BNIs and DMPP prevented an increase in the abundance of ammonia-oxidizing bacteria (AOB) without affecting the total bacterial abundance. Both nitrification inhibitors maintained similar soil NH4+ content, but at 30 days post-fertilization (DPF), the sorghum BNIs resulted in higher soil NO3− content than DMPP. Even so, these inhibitors managed to reduce 64% and 96%, respectively, of the NO3−-N/NH4+-N ratio compared to the control treatment. Similar to soil mineral N, there were no differences in leaf δ15N values between the two nitrification inhibitors, yet at 30 DPF, δ15N values from sorghum BNI were more positive than those of DMPP. N2O emissions from DMPP-treated soil were low throughout the experiment. Nevertheless, while sorghum BNIs also maintained low N2O emissions, they were associated with a substantial N2O emission peak at 3 DPF that lasted until 7 DPF. Conclusions: Our results indicate that while sorghum root exudates can reduce nitrification in field soil, even at the same efficiency as DMPP for a certain amount of time, they are not able to prevent the N pollution derived from N fertilization as DMPP does during the entire experiment.
Open Access
Evidences towards deciphering the mode of action of dimethylpyrazole-based nitrification inhibitors in soil and pure cultures of Nitrosomonas europaea
(Springer, 2022) Bozal-Leorri, Adrián; Corrochano Monsalve, Mario; Vega-Mas, Izargi; Aparicio Tejo, Pedro María; González Murua, Carmen; Marino, Daniel; Institute for Multidisciplinary Research in Applied Biology - IMAB
Background: Agriculture relies on the intensive use of synthetic nitrogen (N) fertilizers to maximize crop yields, which has led to the transformation of agricultural soils into high-nitrifying environments. Nevertheless, nitrifcation inhibitors (NIs) have been developed to suppress soil-nitrifer activity and decrease N losses. The NIs 3,4-dimethyl‑ pyrazole phosphate (DMPP) and 2-(3,4-dimethyl-1H-pyrazol-1-yl) succinic acid isomeric mixture (DMPSA) are able to reduce N2O emissions and maintain soil NH4 + for a longer time. Although both NIs have been proven to be efective to inhibit soil nitrifcation, their exact mode of action has not been confrmed. We aimed to provide novel insights to further understand the mode of action of DMP-based NIs. We evaluated the performance of DMPP and DMPSA in soil and pure cultures of nitrifying bacteria Nitrosomonas europaea. Results: DMPSA did not inhibit nitrifcation in pure cultures of N. europaea. In the soil, we evidenced that DMPSA needs to be broken into DMP to achieve the inhibition of nitrifcation, which is mediated by a soil biological process that remains to be identifed. Moreover, both DMPP and DMPSA are thought to inhibit nitrifcation due to their ability to chelate the Cu2+ cations that the ammonia monooxygenase enzyme (AMO) needs to carry on the frst step of NH4 + oxidation. However, the efciency of DMPP was not altered regardless the Cu2+ concentration in the medium. In addition, we also showed that DMPP targets AMO but not hydroxylamine oxidoreductase enzyme (HAO). Conclusions: The inability of DMPSA to inhibit nitrifcation in pure cultures together with the high efciency of DMPP to inhibit nitrifcation even in presence of toxic Cu2+ concentration in the medium, suggest that the mode of action of DMP-based NIs does not rely on their capacity as metal chelators.

Aparicio Tejo, Pedro María

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