Nitrous oxide (N₂O) emissions have been increasing as a result of intensive nitrogen (N) fertilisation. Soil nitrification and denitrification are the main sources of N₂O, and the use of ammonium-based fertilisers combined with nitrification inhibitors (NIs) could be useful in mitigating N₂O emissions from agricultural systems. In this work we looked at the N₂O mitigation capacity of two dimethylpyrazol-based NIs, 3,4-dimethylpyrazole phosphate (DMPP) and 2-(N-3,4-dimethyl-1H-pyrazol-1-yl) succinic acid isomeric mixture (DMPSA), on soil nitrifying and denitrifying microbial populations under two contrasting soil water contents (40% and 80% soil water filled pore space; WFPS). Our results show that DMPP and DMPSA are equally efficient at reducing N₂O emissions under 40% WFPS conditions by inhibiting bacterial ammonia oxidation. In contrast, at 80% WFPS DMPSA was less efficient than DMPP at reducing N₂O emissions. Interestingly, at 80% WFPS, where lowered oxygen availability limits nitrification, both DMPP and DMPSA not only inhibited nitrification but also stimulated N₂O reduction to molecular nitrogen (N₂) via nitrous oxide reductase activity (Nos activity). Therefore, in this work we observed that DMP-based NIs stimulated the reduction of N₂O to N₂by nitrous oxide reductase during the denitrification process.

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.

Common bean (Phaseolus vulgaris L.), one of the most important legume crops, uses atmospheric nitrogen through symbiosis with soil rhizobia, reducing the need for nitrogen fertilization. However, this legume is particularly sensitive to drought conditions, prevalent in arid regions where this crop is cultured. Therefore, studying the response to drought is important to sustain crop productivity. We have used integrated transcriptomic and metabolomic analysis to understand the molecular responses to water deficit in a marker-class common bean accession cultivated under N₂ fixation or fertilized with nitrate (NO₃^–). RNA-seq revealed more transcriptional changes in the plants fertilized with NO₃^– than in the N₂-fixing plants. However, changes in N₂-fixing plants were more associated with drought tolerance than in those fertilized with NO₃^–. N₂-fixing plants accumulated more ureides in response to drought, and GC/MS and LC/MS analysis of primary and secondary metabolite profiles revealed that N₂-fixing plants also had higher levels of abscisic acid, proline, raffinose, amino acids, sphingolipids, and triacylglycerols than those fertilized with NO₃^–. Moreover, plants grown under nitrogen fixation recovered from drought better than plants fertilized with NO₃^–. Altogether we show that common bean plants grown under symbiotic nitrogen fixation were more protected against drought than the plants fertilized with nitrate.

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.

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.