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
Soil moisture modulates biological nitrification inhibitors release in sorghum plants
(Springer, 2023) Bozal-Leorri, Adrián; Arregui Odériz, Luis Miguel; Torralbo, Fernando; González Moro, María Begoña; González Murua, Carmen; Aparicio Tejo, Pedro María; Institute on Innovation and Sustainable Development in Food Chain - ISFOOD; Institute for Multidisciplinary Research in Applied Biology - IMAB
Background and aims: Sorghum (Sorghum bicolor) is able to exude allelochemicals with biological nitrifcation inhibition (BNI) capacity. Therefore, sorghum might be an option as cover crop since its BNI ability may reduce N pollution in the following crop due to a decreased nitrifcation. However, BNI exudation is related to the physiological state and development of the plant, so abiotic stresses such as drought might modify the rate of BNI exudation. Hence, the objective was to determine the efect of drought stress on sorghum plants’ BNI release. Methods: The residual efects of sorghum crops over ammonia-oxidizing bacteria (AOB) were monitored in a 3-year feld experiment. In a controlled-conditions experiment, sorghum plants were grown under Watered (60% WFPS) or Moderate drought (30% WFPS) conditions, and fertilized with ammonium sulphate (A), ammonium sulphate+DMPP (A+D), or potassium nitrate (KNO3 −). Soil mineral N was determined, and AOB populations were quantifed. Additionally, plant biomass, isotopic discrimination of N and C, and photosynthetic parameters were measured in sorghum plants. Results: In the driest year, sorghum was able to reduce the AOB relative abundance by 50% at feld conditions. In the plant-soil microcosm, drought stress reduced leaf photosynthetic parameters, which had an impact on plant biomass. Under these conditions, sorghum plants exposed to Moderate drought reduced the AOB abundance of A treatment by 25% compared to Watered treatment. Conclusion: The release of BNI by sorghum under limited water conditions might ensure high soil NH4 +-N pool for crop uptake due to a reduction of nitrifying microorganisms.
Open Access
Assessing the efficiency of dimethylpyrazole-based nitrification inhibitors under elevated CO2 conditions
(Elsevier, 2021) Bozal-Leorri, Adrián; González Murua, Carmen; Marino Bilbao, Daniel; Aparicio Tejo, Pedro María; Corrochano Monsalve, Mario; Institute for Multidisciplinary Research in Applied Biology - IMAB
Nitrification inhibitors (NIs) are useful tools to reduce nitrogen (N) losses derived from fertilization in agriculture. However, it remains unclear whether a future climate scenario with elevated CO2 could affect NIs efficiency. Thus, the objective of this work was to study whether the increase of atmospheric CO2 concentration would affect the efficiency of two dimethylpyrazole-based NIs: 3,4-dimethylpyrazol phosphate (DMPP) and 3,4-dimethylpyrazol succinic acid (DMPSA) in a plant-soil microcosm. To do so, Hordeum vulgare var. Henley plants were grown in soil fertilized with ammonium sulphate (AS) with or without NIs under controlled environmental conditions at ambient CO2 (aCO(2)) or elevated CO2 (eCO(2); 700 ppm). In the soil, mineral nitrogen and N2O emission evolution were monitored together with nitrifying and denitrifying population that were quantified by qPCR. In the plant, biomass, total amino acid content and isotopic discrimination of N and C were measured. Both NIs showed greater efficiency to maintain soil NH4+ content under eCO(2) compared to aCO(2), as a consequence of 80% reduction of AOB abundance in eCO(2). Indeed, both inhibitors were able to lessen 53% the N2O emissions in eCO(2) compared to aCO(2). Regarding the plant, DMPP and DMPSA negatively affected plant biomass at aCO(2) but this effect was restored at eCO(2) due to a better ammonium tolerance associated with an increase in total amino acid content. Overall, DMPP and DMPSA NIs were highly efficient under eCO(2), reducing N2O emissions and keeping N in the soil stable for longer while maintaining plant biomass production.
Open Access
Evaluation of a crop rotation with biological inhibition potential to avoid N2O emissions in comparison with synthetic nitrification inhibition
(Elsevier, 2023) Bozal-Leorri, Adrián; Corrochano Monsalve, Mario; Arregui Odériz, Luis Miguel; Aparicio Tejo, Pedro María; González Murua, Carmen; Institute on Innovation and Sustainable Development in Food Chain - ISFOOD; Institute for Multidisciplinary Research in Applied Biology - IMAB
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
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.
Open Access
Short-term exposure to high atmospheric vapor pressure deficit (Vpd) severely impacts durum wheat carbon and nitrogen metabolism in the absence of edaphic water stress
(MDPI, 2021) Fakhet, Dorra; Morales Iribas, Fermín; Jáuregui Mosquera, Iván; Erice, G.; Aparicio Tejo, Pedro María; González Murua, Carmen; Aranjuelo Michelena, Iker; Aroca, Ricardo; Irigoyen, Juan J.; Ciencias; Zientziak
Low atmospheric relative humidity (RH) accompanied by elevated air temperature and decreased precipitation are environmental challenges that wheat production will face in future decades. These changes to the atmosphere are causing increases in air vapor pressure deficit (VPD) and low soil water availability during certain periods of the wheat-growing season. The main objective of this study was to analyze the physiological, metabolic, and transcriptional response of carbon (C) and nitrogen (N) metabolism of wheat (Triticum durum cv. Sula) to increases in VPD and soil water stress conditions, either alone or in combination. Plants were first grown in well-watered conditions and near-ambient temperature and RH in temperature-gradient greenhouses until anthesis, and they were then subjected to two different water regimes well-watered (WW) and water-stressed (WS), i.e., watered at 50% of the control for one week, followed by two VPD levels (low, 1.01/0.36 KPa and high, 2.27/0.62 KPa; day/night) for five additional days. Both VPD and soil water content had an important impact on water status and the plant physiological apparatus. While high VPD and water stress-induced stomatal closure affected photosynthetic rates, in the case of plants watered at 50%, high VPD also caused a direct impairment of the RuBisCO large subunit, RuBisCO activase and the electron transport rate. Regarding N metabolism, the gene expression, nitrite reductase (NIR) and transport levels detected in young leaves, as well as determinations of the δ15N and amino acid profiles (arginine, leucine, tryptophan, aspartic acid, and serine) indicated activation of N metabolism and final transport of nitrate to leaves and photosynthesizing cells. On the other hand, under low VPD conditions, a positive effect was only observed on gene expression related to the final step of nitrate supply to photosynthesizing cells, whereas the amount of15N supplied to the roots that reached the leaves decreased. Such an effect would suggest an impaired N remobilization from other organs to young leaves under water stress conditions and low VPD.