Search

Background and aims Sorghum (Sorghum bicolor) is able to exude allelochemicals with biological nitrification 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 nitrification. 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 effect of drought stress on sorghum plants’ BNI release. Methods The residual effects of sorghum crops over ammonia-oxidizing bacteria (AOB) were monitored in a 3-year field 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 quantified. 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 field 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.

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. This work was supported by the Spanish Government (RTI2018-094623-B-C21 and C22 MCIU/AEI/FEDER, UE) and the Basque Government (IT-932-16). Dr. Adrián Bozal-Leorri held a grant from the Basque Government (PRE-2020-2-0142). Dr. Mario Corrochano-Monsalve held a grant from the Ministry of Economy and Business of the Spanish Government (BES-2016-076725).

Nutrition is one of the factors that most limits forestry plant growth; thus, current production in nurseries is based on conventional fertilization focused on enhancing vigor. However, an excessive intake of mineral nitrogen can cause morphological imbalances and the formation of more succulent tissues which, consequently, increase susceptibility to plant pathogens. Fusarium circinatum is the causal agent of pitch canker in plants of the Pinus genus, with Pinus radiata being the species most susceptible to this disease. This study compares the response of P. radiata seedlings to infection by F. circinatum as influenced by two fertilizers—conventional and aerated compost tea (ACT)—applied during the nursery phase. The potential of ACT against F. circinatum was first tested in vitro, where it was found to inhibit the pathogen’s mycelial growth and conidial germination. In the greenhouse, infected plants fertilized with ACT exhibited less severe internal and external symptoms of pitch canker and lower levels of pathogen colonization of both stems and needles than with conventional fertilizer. An analysis of the hormone content and defense-related gene expression shows greater salicylic acid production and phenylalanine ammonium-lyase and chalcone synthase expression in ACT-fertilized pine. All of the parameters assessed are consistent in showing that biofertilization with ACT reduces the susceptibility of pine seedlings to the disease compared with conventional fertilization.

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 N

[EN]Nitrogen fertilization is the most important factor increasing nitrous oxide (N2O) emissions from agriculture, which is a powerful greenhouse gas. These emissions are mainly produced by the soil microbial processes of nitrification and denitrification, and the application of nitrification inhibitors (NIs) together with an ammonium-based fertilizer has been proved as an efficient way to decrease them. In this work the NIs dimethylpyrazole phosphate (DMPP) and dimethylpyrazole succinic acid (DMPSA) were evaluated in a temperate grassland under environmental changing field conditions in terms of their efficiency reducing N2O emissions and their effect on the amount of nitrifying and denitrifying bacterial populations responsible of these emissions. The stimulation of nitrifying bacteria induced by the application of ammonium sulphate as fertilizer was efficiently avoided by the application of both DMPP and DMPSA whatever the soil water content. The denitrifying bacteria population capable of reducing N2O up to N-2 was also enhanced by both NIs provided that sufficiently high soil water conditions and low nitrate content were occurring. Therefore, both NIs showed the capacity to promote the denitrification process up to N-2 as a mechanism to mitigate N2O emissions. DMPSA proved to be a promising NI, since it showed a more significant effect than DMPP in decreasing N2O emissions and increasing ryegrass yield. This work was funded by the Spanish Government (AGL2015-64582-C3-2-R MINECO/FEDER and RTI2018-094623-B-C21 MCIU/AEI/FEDER, UE) , by the Basque Government (IT-932-16) and by EuroChem Agro Iberia S.L.-UPV/EHU 2015.0248 and 2016.0339. Ximena Huerfano was recipient of a specialization fellowship from the UPV/EHU for Ph.D. researchers.

Significance Globally, wheat farming is a major source of nitrogen pollution. Rapid generation of soil nitrates cause nitrogen leakage and damage ecosystems and human health. Here, we show the 3NsbS chromosome arm in wild grass (Leymus racemosus) that controls root nitrification inhibitor production can be transferred into elite wheat cultivars, without disrupting the elite agronomic features. Biological nitrification inhibition (BNI)–enabled wheats can improve soil ammonium levels by slowing down its oxidation and generate significant synergistic benefits from assimilating dual nitrogen forms and improving adaptation to low N systems. Deploying BNI-enabled wheat on a significant proportion of current global wheat area (ca. 225 M ha) could be a powerful nature-based solution for reducing N fertilizer use and nitrogen losses while maintaining productivity., 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.

Nitrogen fertilization is a major force in global greenhouse gases emissions and causes environmental contamination through nitrate leaching. The use of nitrification inhibitors has been proven successful to mitigate these effects. However, there is an increasing concern about the undesired effects that their potential persistence in the soil or accumulation in plants may provoke. In this study, we first exposed Lotus japonicus plants to high amounts of 3,4 dimethylpyrazole phosphate (DMPP) and 2-(N-3,4-dimethyl-1H-pyrazol-1-yl) succinic acid isomeric mixture (DMPSA) nitrification inhibitors. Exposure to doses higher than 1 mg·L−1 provoked DMPP accumulation mostly in the aerial part, while DMPSA was only detected from 10 mg·L−1 and nearly no translocation. To evaluate the effect that DMPP accumulation in leaves may provoke on plant performance we combined a transcriptome, proteome, and physiological analysis in plants treated with 10 mg/ L of DMPP. This treatment provoked changes in the expression of 229 genes and 59 proteins. Overall, we evidence that when DMPP accumulates in leaves it induces stress responses, notably provoking changes in cell redox balance, hormone signaling, protein synthesis and turnover and carbon and nitrogen metabolism.

Nitrogen fertilization is the most important factor increasing nitrous oxide (N

In forest nurseries, intensive use of non-renewable substrates such as peat and high application rates of chemical synthesis fertilizers lead to environmental problems and high susceptibility to biotic and abiotic stresses. This work aims to seek more sustainable crop management to help mitigate these problems, combining the substitution of peat by compost and the use of growth-promoting microorganisms (PGPs) as a fertilization tool. For this purpose, a trial was carried out to test the effectiveness of an agricultural waste compost and a biostimulant based on PGP microorganisms in the production of Castanea sativa plants in a forest nursery. This trial assessed the growth of plants, with both inputs separately and combined, and then studied the tolerance of chestnut seedlings to water deficit. The results showed that partial substitution of peat by compost is possible, but not complete, as the high levels of conductivity and pH generated by a high proportion of compost negatively affected plant growth. It was also noted that the application of the biostimulant enables the complete substitution of mineral fertilization. Moreover, at the end of the nursery phase, chestnut seedlings treated with the biostimulant showed the same or even better quality than chestnut seedlings obtained with conventional fertilization, also resulting in greater resistance to water deficit, based on the increase in root volume and the improvement of the physiological status. Changes observed in both quantity and composition of microbiota associated with chestnut rhizosphere after inoculation with PGPs were related to the improvement observed. In relation to water deficit resistance, a positive synergy was also observed with the combination of both inputs, since plants with full substitution of peat by compost combined with PGP-based fertilization showed the greatest drought resistance. This work was funded by the Spanish Government (RTI2018-094623-B-C21 MCIU/AEI/FEDER, UE), and by the Basque Government (IT-932-16).

Improving fertilizer nitrogen (N) use efficiency is essential to increase crop productivity and avoid environmental damage. This study was conducted during four crop cycles of winter wheat under humid Mediterranean conditions (Araba, northern Spain). The effects of N-fertilization splitting and the application of the nitrification inhibitors (NIs) 3,4-dimethylpyrazole phosphate (DMPP) and 2-(3,4-dimethyl-1H-pyrazol-1-yl) succinic acid isomeric mixture (DMPSA) as strategies to improve grain quality were examined. The hypothesis of this study was to test if the partial ammonium nutrition and the reduction of fertilizer losses presumably induced by the application of NIs can modify the grain gliadin and glutenin protein contents and the breadmaking quality (dough rheological properties). Among both NIs assayed, only DMPP showed a slight effect of decreasing the omega gliadin fraction, following splitting either two or three times, although this effect was dependent on the year and was not reflected in terms of dough extensibility. The slight decreases observed in grain quality in terms of dough strength and glutenin content induced by DMPP suggest that DMPSA is more promising in terms of maintaining grain quality. Nonetheless, these poor effects exerted by NI application on grain quality parameters did not lead to changes in the quality parameters defining the flour aptitudes for breadmaking. This research was funded by the Basque Government (IT 932-16), by the Spanish Government (RTA2009 00028 C03 03, AGL2012 37815 C05 02 and AGL2015 64582 C3 2 R MINECO/FEDER) and by EuroChem Agro Iberia S.L.–UPV/EHU 2011.0051, 2012.0007, 2013.0001 and 2014.0002, Ximena Huérfano received a specialization fellowship for PhD researchers from the UPV/EHU.

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 of 15N 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., This work was supported by the Spanish Innovation and Universities Ministry (AGL2016-79868-R; 427 PCIN-2017-007) and the Basque Country Government consolidated group program (IT-932-16).

[EN] Nitrogen (N) input from fertilizers modifies the properties of agricultural soils as well as bacterial community diversity, composition and relationships. This can lead to negative impacts such as the deterioration of system multifunctionality, whose maintenance is critical to normal nutrient cycling. Synthetic nitrification inhibitors (NIs) can be combined with fertilizers to improve the efficiency of N use by reducing N losses. However, analysis of their effects on non-target bacteria are scarce. This study aimed to analyze the effect of applying the NIs DMPP and DMPSA on the whole bacterial community. Through 16S rRNA amplicon sequencing we determined the differences between samples in terms of microbial diversity, composition and co-occurrence networks. The application ofDMPP and DMPSA exerted little impact on the abundance of the dominant phyla. Nevertheless, several significant shifts were detected in bacterial diversity, co-occurrence networks, and the abundance of particular taxa, where soil water content played a key role. For instance, the application of NIs intensified the negative impact of N fertilization on bacterial diversity under high water-filled pore spaces (WFPS) (>64%), reducing community diversity, whereas alpha-diversity was not affected at low WFPS (

Nitrate and ammonium are the main nitrogen sources in agricultural soils. In the last decade, ammonium (NH4+), a double-sided metabolite, has attracted considerable attention by researchers. Its ubiquitous presence in plant metabolism and its metabolic energy economy for being assimilated contrast with its toxicity when present in high amounts in the external medium. Plant species can adopt different strategies to maintain NH4+ homeostasis, as the maximization of its compartmentalization and assimilation in organic compounds, primarily as amino acids and proteins. In the present study, we report an integrative metabolic response to ammonium nutrition of seven plant species, belonging to four different families: Gramineae (ryegrass, wheat, Brachypodium distachyon), Leguminosae (clover), Solanaceae (tomato), and Brassicaceae (oilseed rape, Arabidopsis thaliana). We use principal component analysis (PCA) and correlations among metabolic and biochemical data from 40 experimental conditions to understand the whole-plant response. The nature of main amino acids is analyzed among species, under the hypothesis that those Asn-accumulating species will show a better response to ammonium nutrition. Given the provision of carbon (C) skeletons is crucial for promotion of the nitrogen assimilation, the role of different anaplerotic enzymes is discussed in relation to ammonium nutrition at a whole-plant level. Among these enzymes, isocitrate dehydrogenase (ICDH) shows to be a good candidate to increase nitrogen assimilation in plants. Overall, metabolic adaptation of different carbon anaplerotic activities is linked with the preference to synthesize Asn or Gln in their organs. Lastly, glutamate dehydrogenase (GDH) reveals as an important enzyme to surpass C limitation during ammonium assimilation in roots, with a disparate collaboration of glutamine synthetase (GS). The design of the study, analysis, and interpretation of data and writing of the manuscript was supported by the Basque Government [IT932-16] or GIC15/179, the Spanish Ministry of Economy and Competitiveness [AGL2015-64582-C3-2-R] and [BIO2017-84035-R]. IVM held a postdoctoral grant from the Basque Government (conv. 2018) and MDLP held a PhD grant by COLCIENCIAS (conv. 672).

RNA-based high-throughput sequencing is a valuable tool in the discernment of the implication of metabolically active bacteria during composting. In this study, “alperujo” composting was used as microbial model for the elucidation of structure-function relationships with physicochemical transformation of the organic matter. DNA and RNA, subsequently retrotranscribed into cDNA, were isolated at the mesophilic, thermophilic and maturation phases. 16S rRNA gene was amplified by quantitative PCR (qPCR) and Illumina MiSeq platform to assess bacterial abundance and diversity, respectively. The results showed that the abundance of active bacteria assessed by qPCR was maximum at thermophilic phase, which confirm it as the most active stage of the process. Concerning diversity, Proteobacteria, Firmicutes, Bacteroidetes and Actinobacteria were the main phyla presented in composts. Concomitantly, three different behaviours were observed for bacterial dynamics: some genera decreased during the whole process meanwhile others proliferated only at thermophilic or maturation phase. Statistical correlation between physicochemical transformations of the organic matter and bacterial diversity revealed bacterial specialisation. This result indicated that specific groups of bacteria were only involved in the organic matter degradation during bio-oxidative phase or humification at maturation. Metabolic functions predictions confirmed that active bacteria were mainly involved in carbon (C) and nitrogen (N) cycles transformations, and pathogen reduction., This work was supported by the ERDF-co-financed projects from Junta de Andalucía (Spain) [P12-AGR-1968], Spanish MINECO [AGL2015-64582-CO3-02, AGL2017-84745-R] and MINECO-CSIC RECUPERA 2020 [20134R070]. G. Tortosa thanks the farmer J. González Almendros for his financial and technical assistance during AL composting. Support by Basque Country Government [IT-583 932-16] and the Spanish Red Sirena [AGL2015-68881-REDT] are also acknowledged. E. Aranda thanks MINECO-ERDF for supporting her Ramón y Cajal project [RYC-2013-12481] and [CTM2017-84332-R].

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. This project was funded by the Spanish Government (RTI2018-094623-B-C21 MCIU/AEI/FEDER, UE) and by the Basque Government (IT-932-16). Adrian Bozal-Leorri holds a grant from the Basque Government. Mario Corrochano-Monsalve holds a grant from the Ministry of Economy and Business of the Spanish Government (BES-2016-076725).

The Lluta Valley in Northern Chile is an important agricultural area affected by both salinity and boron (B) toxicity. Zea mays L. amylacea, an ecotype arisen because of the seed selection practiced in this valley, shows a high tolerance to salt and B levels. In the present study the interaction between B and salt was studied after 20 days of treatment at low (100 mM) and high salinity (430 mM NaCl), assessing changes in nitrogen metabolites and in the activity of key nitrogen-assimilating enzymes. Under non-saline conditions, the presence of excessive B favored higher nitrate and ammonium mobilization to leaves, increasing nitrate reductase (NR) activity but not glutamine synthetase (GS). Thus, the increment of nitrogen use efficiency by B application would contribute partially to maintain the biomass production in this ecotype. Positive relationships between NR activity, nitrate, and stomatal conductance were observed in leaves. The increment of major amino acids alanine and serine would indicate a photoprotective role of photorespiration under low-salinity conditions, thus the inhibition of nitrogen assimilation pathway (NR and GS activities) occurred only at high salinity. The role of cytosolic GS regarding the proline accumulation is discussed. Research funded by The Basque Government (IT932-1). E.I. Bastías received a pre-doctoral fellowship from the Universidad de Tarapacá (Arica, Chile) and financial support by Convenio Desempeño Regional UTA-1795.

Agricultural sustainability is compromised by nitrogen (N) losses caused by soil microbial activity. Nitrous oxide (N2O) is a potent greenhouse gas (GHG) produced as consequence of nitrification and denitrification processes in soils. Nitrification inhibitors (NI) as 3,4-dimethylpyrazole-succinic acid (DMPSA) are useful tools to reduce these N losses from fertilization. The objective of this work was to test the efficiency of DMPSA in two different tillage management systems, conventional tillage (CT) and no-tillage (NT), in a winter wheat crop under Humid Mediterranean conditions. N fertilizer was applied as ammonium sulphate (AS) with or without DMPSA in a single or split application, including an unfertilized treatment. GHG fluxes N2O, CO2 and CH4) were measured by the closed chamber method. amoA and nosZl genes were quantified by qPCR as indicators of nitrifying and denitrifying populations. Nitrification was inhibited by DMPSA in both CT and NT, while the higher water filled pore space (WFPS) in NT promoted a better efficiency of DMPSA in this system. This higher efficiency might be due to a greater N2O reduction to N-2 as result of the nosZl gene induction. Consequently, DMPSA was able to reduce N2O emissions down to the unfertilized levels in NT. Provided that NT reduced CO2 emissions and maintained crop yield compared to CT, the application DMPSA under NT management is a promising strategy to increase agro-systems sustainability under Humid Mediterranean conditions. (C) 2019 The Author(s). Published by Elsevier B.V. This project was funded by de Spanish Government (AGL2015-64582-C3-2-R MINECO/FEDER and RTI2018-094623-B-C21 MCIU/AEI/FEDER, UE), by the Basque Government (IT-932-16) and by EuroChem Agro Iberia S.L.-UPV/EHU 2017.0016. Mario Corrochano-Monsalve held a grant from the Ministry of Economy and Business of the Spanish Government and Ximena Huerfano received a specialization fellowship for PhD researches from the UPV/EHU.

Metagenomic and transcriptomic techniques applied to composting could increase our understanding of the overall microbial ecology and could help us to optimise operational conditions which are directly related with economic interest. In this study, the fungal diversity and abundance of two-phase olive mill waste (“alperujo”) composting was studied using Illumina MiSeq sequencing and quantitative PCR, respectively. The results showed an increase of the fungal diversity during the process, with Ascomycota being the predominant phylum. Penicillium was the main genera identified at the mesophilic and maturation phases, with Debaryomyces and Sarocladium at the thermophilic phase, respectively. The fungal abundance was increased during composting, which confirms their important role during thermophilic and maturation phases. Some Basidiomycota showed an increased during the process, which showed a positive correlation with the humification parameters. According to that, the genus Cystofilobasidium could be used as a potential fungal biomarker to assess alperujo compost maturation., This work was supported by the ERDF-co-financed projects from Junta de Andalucía (Spain) [P12-AGR-1968], the Spanish MINECO [AGL2015-64582-CO3-02] and MINECO-CSIC RECUPERA 2020 [20134R070]. G. Tortosa thanks the farmer J. González Almendros for his financial and technical assistance during AL composting and also, A. J. Fernández-González, A. Vicente-Lasa, M. Fernández-López and P. J. Villadas for their helpful discussions. Support by Basque Country Government [IT-583 932-16] and the Spanish Red Sirena [AGL2015-68881-REDT] are also acknowledged. E. Aranda thanks MINECO-ERDF for supporting her Ramón y Cajal project [RYC-2013-12481] and [CTM2017-84332-R].

This chapter presents a study of nitrous oxide (N2O) emissions from (a) forest soils (Pinus radiata and Fagus sylvatica) at different growth stages and from (b) grassland and agricultural soils in the edapho-climatic conditions of northern Spain. A mixed clover–ryegrass sward, wheat and oats crops were fertilized with ammonium sulphate nitrate, cattle slurry and/or sewage sludge. The mitigation effectiveness of the nitrification inhibitor (NI) 3,4-dimethylpyrazole phosphate (DMPP) was also assayed. Nitrous oxide losses from forests in northern Spain are limited by nitrogen (N) deposition, resulting in lower losses than temperate forest in the rest of Europe. The NI DMPP seems to be an advisable strategy to mitigate N2O emissions, both in grasslands and in crops. Sewage sludge application should be further studied but significant reduction in N2O emission is possible with DMPP. The results presented suggest that an emission factor around 0.1–0.3%, depending on crop type, time of year and fertilizer type, should be applied for this area instead of the default value of 1% suggested by the Intergovernmental Panel on Climate Change (IPCC).

The increase of the global demand for dairy products is reflected in a rise of animal feed and forage productivity. In the coastal Atlantic climate conditions of northern Spain the maize-ryegrass rotation is a common management used to satisfy this forage demand. With the aim of mitigating greenhouse gases (GHG) emissions associated with fertilization in this type of intensive management, the use of nitrification inhibitors (NI) such as 3,4-dimethylpyrazol phosphate (DMPP) or the isomeric mixture of 2-(3,4-dimethyl-1H-pyrazol-1-yl) succinic acid and 2-(4,5-dimethyl-1H-pyrazol-1-yl) succinic acid (DMPSA) could be a useful strategy. Until now, the new NI DMPSA has only been evaluated under Mediterranean conditions. The objective of this study was to compare the efficiency of DMPSA with respect to DMPP reducing GHG emissions when applied in a maize-ryegrass rotation under Atlantic climate conditions. Nitrogen fertilizer was applied as ammonium sulphate, with and without both NIs, split into two applications of 80 and 100 kg N ha−1 in the case of maize and in three applications of 80, 60 and 60 kg N ha−1 in the case of ryegrass. An unfertilized control treatment was also included. Nitrous oxide (N2O) and methane (CH4) fluxes were measured using the closed chamber technique. The new NI DMPSA showed a similar behaviour to DMPP, mitigating N2O emissions down to the levels of the unfertilized soil. The effect of DMPSA reducing N2O losses lasted for the same time as for DMPP (l

In the last decades, intensive agriculture management and the application of nitrogen fertilizer have led to high nitrogen losses to the environment. Among these losses is the soil emission of the potent greenhouse gas nitrous oxide (N 2 O) which is mainly produced by the soil microbial processes of nitrification and denitrification. The use of nitrification inhibitors with ammonium based fertilizers can be an efficient mitigation strategy to decrease these nitrogen losses. Soil water content and temperature are major factors controlling N 2 O production and, so, also the efficiency of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) to reduce these emissions. In this work we study the effect of soil water content and temperature on the abundance of soil bacteria, ammonia-oxidizing bacteria and denitrifying bacteria, and on the performance of DMPP modulating these different bacterial populations responsible for N 2 O production/consumption. The effect of DMPP on the abundance of the different bacterial populations was dependent on soil water content. Under 40% of soil water filled pore space (WFPS), the application of DMPP caused an expected decrease of the target amoA gene abundance while narG , nirK and nosZ gene abundances also decreased probably due to an indirect effect induced by the lack of substrate for denitrifiers. Under 80% of WFPS, while the application of DMPP did not induce any change in the amoA gene abundance, an unexpected increase in non-target denitrifying gene abundances ( narG, nirK and nosZ ) was observed at either 10 °C or 20 °C incubation temperatures. This finding opens a new gate of research in the use of DMPP, where nitrous oxide reductase enzyme gene ( nosZ ) abundance and expression should be studied in the future in order to better understand the performance of DMPP not only inhibiting nitrification, but also affecting the non-target denitrification process.

The increase in the atmospheric CO

The increase in the atmospheric CO concentration is predicted to influence wheat production and grain quality and nutritional properties. In the present study, durum wheat (Triticum durum Desf. cv. Sula) was grown under two different CO (400 versus 700 μmol mol) concentrations to examine effects on the crop yield and grain quality at different phenological stages (from grain filling to maturity). Exposure to elevated CO significantly increased aboveground biomass and grain yield components. Growth at elevated CO diminished the elemental N content as well as protein and free amino acids, with a typical decrease in glutamine, which is the most represented amino acid in grain proteins. Such a general decrease in nitrogenous compounds was associated with altered kinetics of protein accumulation, N remobilization, and N partitioning. Our results highlight important modifications of grain metabolism that have implications for its nutritional quality., This work was supported by the Spanish Ministry of Science and Innovation (AGL2016-79868-R).

Proper carbon (C) supply is essential for nitrogen (N) assimilation especially when plants are grown under ammonium (NH4+) nutrition. However, how C and N metabolic fluxes adapt to achieve so remains uncertain. In this work, roots of wheat (Triticum aestivum L.) plants grown under exclusive NH4+ or nitrate (NO3−) supply were incubated with isotope-labelled substrates (15NH4+, 15NO3−, or [13C]Pyruvate) to follow the incorporation of 15N or 13C into amino acids and organic acids. Roots of plants adapted to ammonium nutrition presented higher capacity to incorporate both 15NH4+ and 15NO3− into amino acids, thanks to the previous induction of the NH4+ assimilative machinery. The 15N label was firstly incorporated into [15N]Gln vía glutamine synthetase; ultimately leading to [15N]Asn accumulation as an optimal NH4+ storage. The provision of [13C]Pyruvate led to [13C]Citrate and [13C]Malate accumulation and to rapid [13C]2-OG consumption for amino acid synthesis and highlighted the importance of the anaplerotic routes associated to tricarboxylic acid (TCA) cycle. Taken together, our results indicate that root adaptation to ammonium nutrition allowed efficient assimilation of N thanks to the promotion of TCA cycle open flux modes in order to sustain C skeleton availability for effective NH4+ detoxification into amino acids.

Anion-exchange FPLC has been used to resolve the isoforms of glutamine synthetase (GS, EC 6.3.1.2) from Zea mays mesophyll (MC) and bundle sheath cells (BSC). Two different isoforms were detected in both types of photosynthetic cells. The predominantly active isoform was GS1 (61%) in MC and GS2 (67%) in BSC. The relative contribution of GS1 and GS2 to the overall GS activity in BSC in maize here reported resembles the proportion described for most C3 plants. Differences among these isoforms in terms of their susceptibility to phosphinothricin (PPT), an analogue of glutamate and known inhibitor of GS, were found. The GS1 isoenzyme from MC was the most sensitive form, being inhibited by 50% at approximately 2.0 μM DL-PPT, whereas the GS2 from BSC presented the highest tolerance to the inhibitor (I50=30 μM). The transferase-to-semibiosynthetic activity ratio for the MC isoforms, which was higher than the ratio for the BSC isoforms, and the differences shown by the isoforms in susceptibility to PPT predict important differences in the biochemical properties and regulation of GS isoenzymes. In this regard, the cytoplasmic isoenzymes, and especially the one in MC, due to its relatively high contribution to mesophyll cell GS activity, could play a vital role in nitrogen metabolism in maize.

Grasslands are subject to a wide range of land management practices that influence the exchange of the three main agricultural greenhouse gases (GHGs) that are related to agriculture: carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4). Improving nitrogen fertilization management practices through the use of nitrification inhibitors (NIs) can reduce GHGs emissions. We conducted a field experiment at the Colombian Agricultural Research Corporation with four fertilization treatments: urea (typical fertilizer used in this region), ammonium sulfate nitrate (ASN), ASN plus the NI 3,4-dimethylpyrazole phosphate (ASN+DMPP), and an unfertilized control. The highest grassland yields (1956 and 2057 kg DM ha&minus, 1, respectively) and apparent fertilizer nitrogen recoveries (34% and 33%, respectively) were generated by the conventional urea fertilizer and ASN+DMPP. Furthermore, the use of ASN+DMPP reduced the N2O emissions that were related to N fertilization to the level of the unfertilized treatment (ca. 1.5 g N2O-N ha&minus, 1), with a significant reduction of N-yield-scaled N2O emissions (ca. 20 g N2O-N kg N uptake&minus, 1). These results support the application of DMPP as an alternative strategy to increase grassland yield while simultaneously reducing the environmental impact of N fertilization.

Among strategies suggested to decrease agricultural soil N2O losses, the use of nitrification inhibitors such as DMPP (3,4-dimethylpyrazole phosphate) has been proposed. However, the efficiency of DMPP might be affected by soil amendments, such as biochar, which has been shown to reduce N2O emissions. This study evaluated the synergic effect of a woody biochar applied with DMPP on soil N2O emissions. A incubation study was conducted with a silt loam soil and a biochar obtained from Pinus taeda at 500 degrees C. Two biochar rates (0 and 2% (w/w)) and three different nitrogen treatments (unfertilized, fertilized and fertilized + DMPP) were assayed under two contrasting soil water content levels (40% and 80% of water filled pore space (WFPS)) over a 163 day incubation period. Results showed that DMPP reduced N2O emissions by reducing ammonia-oxidizing bacteria (AOB) populations and promoting the last step of denitrification (measured by the ratio nosZI + nosZII/nirS + nirK genes). Biochar mitigated N2O emissions only at 40% WFPS due to a reduction in AOB population. However, when DMPP was applied to the biochar amended soil, a counteracting effect was observed, since the N2O mitigation induced by DMPP was lower than in control soil, demonstrating that this biochar diminishes the efficiency of the DMPP both at low and high soil water contents. This work was funded by the Spanish Government (AGL2015-64582-C3-2-R MINECO/FEDER), by the Basque Government (IT-932-16) and by the European Union (FACCE-CSA no 276610/MIT04-DESIGN-UPVASC, FACCE-CSA no 2814ERA01A and 2814ERA02A). This work is also supported by the USDA/NIFA Interagency Climate Change Grant Proposal number 2014-02114 [Project number 6657-12130-002-08I, Accession number 1003011] under the Multi-Partner Call on Agricultural Greenhouse Gas Research of the FACCE-Joint Program Initiative. Any opinions, findings, or recommendation expressed in this publication are those of the authors and do not necessarily reflect the view of the USDA. MLC was supported by a Ramon y Cajal contract from the Spanish Ministry of Economy and Competitiveness and thanks Fundacion Seneca for financing the project 19281/PI/14.

While nitrogen (N) derived from ammonium would be energetically less expensive than nitrate-derived N, the use of ammonium-based fertilizer is limited by the potential for toxicity symptoms. Nevertheless, previous studies have shown that exposure to elevated CO2 favors ammonium assimilation in plants. However, little is known about the impact of different forms of N fertilizer on stomatal opening and their consequent effects on CO2 and H2O diffusion in wheat plants exposed to ambient and elevated CO2. In this article, we have examined the response of the photosynthetic machinery of durum wheat (Triticum durum, var. Amilcar) grown with different types of N fertilizer (NO3−, NH4+, and NH4NO3) at 400 versus 700 ppm of CO2. Alongside gas exchange and photochemical parameters, the expression of genes involved in CO2 (PIP1.1 and PIP2.3) and H2O (TIP1) diffusion as well as key C and N primary metabolism enzymes and metabolites were studied. Our results show that at 400 ppm CO2, wheat plants fertilized with ammonium as the N source had stress symptoms and a strong reduction in stomatal conductance, which negatively affected photosynthetic rates. The higher levels of PIP1.1 and PIP2.3 expression in ammonium-fertilized plants at 400 ppm CO2 might reflect the need to overcome limitations to the CO2 supply to chloroplasts due to restrictions in stomatal conductance. This stomatal limitation might be associated with a strategy to reduce ammonium transport toward leaves. On the other hand, ammonium-fertilized plants at elevated CO2 did not show stress symptoms, and no differences were detected in stomatal opening or water use efficiency (WUE). Moreover, similar gene expression of the aquaporins TIP1, PIP1.1, and PIP2.3 in ammonium-fertilized plants grown at 700 ppm compared to nitrate and ammonium nitrate plants would suggest that an adjustment in CO2 and H2O diffusion is not required. Therefore, in the absence of a stress context triggered by elevated CO2, ammonium- and ammonium nitrate-fertilized plants were able to increase their photosynthetic rates, which were translated eventually into higher leaf protein content., Technical support provided by the Phytotron Service, SGIker (UPV/EHU), is gratefully acknowledged. We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI).

Enhanced-efficiency nitrogen (N) fertilizers, such as those containing nitrification or urease inhibitors, can mitigate the carbon (C) footprint linked to the production of bioenergy crops through a reduction in direct nitrous oxide (N2O) emissions and indirect N2O losses. These indirect emissions are derived from ammonia (NH3) volatilization, which also have important environmental and health implications. The evaluation of the global warming potential (GWP) of different N sources using site-specific data of yield and direct and indirect emissions is needed for oilseed rape under rainfed semi-arid conditions, especially when meteorological variability is taken into account. Using urea as a N source, the N2O mitigation efficacy of the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) alone or combined with the nitrification inhibitor 2-(3,4-dimethyl-1H-pyrazol-1-yl) succinic acid isomeric mixture (DMPSA) was evaluated under field conditions in a rainfed oilseed rape (Brassica napus L.) crop. Two additional N sources from calcium ammonium nitrate (CAN), with and without DMPSA, were included. The GWP of the treatments was estimated considering the emissions from inputs, operations and other direct and indirect emissions of greenhouse gases (GHGs), such as methane (CH4) and the volatilization of NH3. We also measured the abundance of key genes involved in nitrification and denitrification to improve the understanding of N2O emissions on a biochemical basis under the conditions of our study. The results show that due to the intense rainfall after fertilization and a rewetting event, N2O losses from fertilizers without inhibitors were greater than those previously reported under Mediterranean conditions, while NH3 losses were low and not affected by the urease inhibitor. The cumulative N2O emissions (which were greatly influenced by a rewetting peak three months after fertilization) from the urea fertilization were significantly higher than those from CAN. The presence of NBPT significantly reduced N2O losses by an average of 71%, with respect to urea. The use of DMPSA with CAN resulted in an abatement of N2O emissions (by 57%) and a significant increase in oil yield in comparison with CAN alone. All inhibitor-based treatments were effective in abating N2O emissions during the rewetting peak. The abundances of the nitrifier and denitrifier communities, especially ammonia-oxidizing bacteria (AOB), significantly decreased relative to the urea or CAN treatments as inhibitors were applied. Under the conditions of our study, the sustainability of a bioenergy crop such as oilseed rape can be improved by using inhibitors because they mitigated N2O emissions and/or enhanced the oil yield.

Urea fertilization is a widely spread source of nitrogen (N) for agriculture because of its easy accessibility. However, its use is highly inefficient, since a large amount of the applied N is lost to the environment mainly in the form of ammonia (NH3) volatilization, causing serious environmental and economic damages. Although there are simple strategies to reduce these losses, as the subsurface application, this practice cannot be adopted in all types of cultivations and tillage systems. To address this problem, combinations of urease and nitrification inhibitors (double inhibitors) have been developed to close all possible N escape routes, which is not achieved when these inhibitors are applied individually. The objective of this work was to evaluate the potential of a new double inhibitor combining N-(n-butyl) thiophosphoric triamide (NBPT) and 2-(3,4-dimethylpyrazole-1-YL)-succinic acid (DMPSA) to mitigate N losses in a rapeseed crop established in conventional tillage (CT) and no-tillage (NT) soils under Humid Mediterranean conditions. To do so, N losses in form of NH3 volatilization and nitrous oxide (N2O) emissions were determined through the Drager-Tube method (DTM) and closed chamber method respectively. The specific weather conditions present during the experiment promoted great losses, mostly in form of NH3 volatilization. The treatments receiving urea without inhibitors or urea with DMPSA lost up to 57.3 and 59.9 kg N ha−1 in CT and NT respectively. Nonetheless, the application of the double inhibitor was able to diminish these losses by more than 50%, reducing the losses to a minimum of 18.8 kg N ha−1 (CT) and 25 kg N ha−1 (NT). As a whole, a CT system fertilized with a single application of urea with the double inhibitor showed the lowest global warming potential (GWP) (3.93 Mg CO2-eq ha−1), at the same level of the unfertilized treatment.

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.

Nowadays agricultural practices are based in the use of N fertilizers which can lead to environmental N losses. These losses can occur as nitrous oxide (N 2 O) emissions as result of the microbial processes of nitrification and denitrification. N 2 O together with carbon dioxide (CO 2 ) and methane (CH 4 ) are the strongest greenhouse gases (GHG) associated with agricultural soils. Nitrification inhibitors (NI) have been developed with the aim of decreasing fertilizer-induced N losses and increasing N efficiency. One of the most popular NI is the 3,4-dimethylpyrazol phosphate (DMPP) which have proven to be an advisable strategy to mitigate GHG emissions while maintaining crops yield. A new NI, 3,4-dimethylpyrazole succinic (DMPSA), has been developed. The objective of this study was to compare the impact of the new nitrification inhibitor DMPSA on greenhouse gases emissions, wheat yield and grain protein with respect to DMPP. For this purpose a field-experiment was carried out for two years. Fertilizer dose, with and without NIs, was 180 kg N ha −1 applied as ammonium sulphate (AS) split in two applications of 60 kg N ha −1 and 120 kg N ha −1 , respectively. A single application of 180 kg N ha −1 of AS with NIs was also made. An unfertilized treatment was also included. The new nitrification inhibitor DMPSA reduces N 2 O emissions up to levels of the unfertilized control treatment maintaining the yield and its components. The DMPSA shows the same behavior as DMPP in relation to N 2 O fluxes, as well as wheat yield and quality. In spite of applying a double dose of N at stem elongation than at tillering, N 2 O losses from that period are lower than at tillering as a consequence of the influence of soil water content and temperature reducing the N 2 O/N 2 ratio by denitrification. NI efficiency in reducing N 2 O losses is determined by the magnitude of the losses from the AS treatment.

Highlight A quantitative proteomic approach demonstrates how ammonium nutrition induces glucosinolate biosynthetic and catabolic pathways in Arabidopsis and broccoli., Accessing different nitrogen (N) sources involves a profound adaptation of plant metabolism. In this study, a quantitative proteomic approach was used to further understand how the model plant Arabidopsis thaliana adjusts to different N sources when grown exclusively under nitrate or ammonium nutrition. Proteome data evidenced that glucosinolate metabolism was differentially regulated by the N source and that both TGG1 and TGG2 myrosinases were more abundant under ammonium nutrition, which is generally considered to be a stressful situation. Moreover, Arabidopsis plants displayed glucosinolate accumulation and induced myrosinase activity under ammonium nutrition. Interestingly, these results were also confirmed in the economically important crop broccoli (Brassica oleracea var. italica). Moreover, these metabolic changes were correlated in Arabidopsis with the differential expression of genes from the aliphatic glucosinolate metabolic pathway. This study underlines the importance of nitrogen nutrition and the potential of using ammonium as the N source in order to stimulate glucosinolate metabolism, which may have important applications not only in terms of reducing pesticide use, but also for increasing plants’ nutritional value.

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 nosZI 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 no-tillage, 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.

In higher plants ammonium (NH4+) assimilation occurs mainly through the glutamine synthetase/glutamate synthase (GS/GOGAT) pathway. Nevertheless, when plants are exposed to stress conditions, such as excess of ammonium, the contribution of alternative routes of ammonium assimilation such as glutamate dehydrogenase (GDH) and asparagine synthetase (AS) activities might serve as detoxification mechanisms. In this work, the in vivo functions of these pathways were studied after supplying an excess of ammonium to tomato (Solanum lycopersicum L. cv. Agora Hybrid F1) roots previously adapted to grow under either nitrate or ammonium nutrition. The short-term incorporation of labelled ammonium (15NH4+) into the main amino acids was determined by GC-MS in the presence or absence of methionine sulphoximine (MSX) and azaserine (AZA), inhibitors of GS and GOGAT activities, respectively. Tomato roots were able to respond rapidly to excess ammonium by enhancing ammonium assimilation regardless of the previous nutritional regime to which the plant was adapted to grow. The assimilation of 15NH4+ could take place through pathways other than GS/GOGAT, since the inhibition of GS and GOGAT did not completely impede the incorporation of the labelled nitrogen into major amino acids. The in vivo formation of Asn by AS was shown to be exclusively Gln-dependent since the root was unable to incorporate 15NH4+ directly into Asn. On the other hand, an in vivo aminating capacity was revealed for GDH, since newly labelled Glu synthesis occurred even when GS and/or GOGAT activities were inhibited. The aminating GDH activity in tomato roots responded to an excess ammonium supply independently of the previous nutritional regime to which the plant had been subjected.

13 páginas, 5 figuras y 2 tablas., Balancing of leaf carbohydrates is a key process for maximising crop performance in elevated CO2 environments. With the aim of testing the role of the carbon sink–source relationship under different CO2 conditions, we performed two experiments with two barley genotypes (Harrington and RCSL-89) exposed to changing CO2. In Experiment 1, the genotypes were exposed to 400 and 700 ppm CO2. Elevated CO2 induced photosynthetic acclimation in Harrington that was linked with the depletion of Rubisco protein. In contrast, a higher peduncle carbohydrate-storage capacity in RSCL-89 was associated with a better balance of leaf carbohydrates that could help to maximize the photosynthetic capacity under elevated CO2. In Experiment 2, plants that were grown at 400 ppm or 700 ppm CO2 for 5 weeks were switched to 700 ppm or 400 ppm CO2, respectively. Raising CO2 to 700 ppm increased photosynthetic rates with a reduction in leaf carbohydrate content and an improvement in N assimilation. The increase in nitrate content was associated with up-regulation of genes of protein transcripts of photosynthesis and N assimilation that favoured plant performance under elevated CO2. Finally, decreasing the CO2 from 700 ppm to 400 ppm revealed that both stomatal closure and inhibited expression of light-harvesting proteins negatively affected photosynthetic performance and plant growth., FT held a PhD grant from the Ministry of Economy and Competitiveness of the Spanish Government. This work was funded by the Spanish Government MINECO/FEDER-UE (AGL2016-79868-R, AGL2016- 79589-R, AGL2015-64582-02-R, AGL2013-41363-R) and by the Basque Government (IT-932-16).