Tomato roots exhibit in vivo glutamate dehydrogenase aminating capacity in response to excess ammonium supply.

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.

Biochar reduces the efficiency of nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) mitigating N2O emissions.

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 °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.

Effect of N-(n-butyl) thiophosphoric triamide and 3,4 dimethylpyrazole phosphate on gaseous emissions from grasslands under different soil water contents.

The intensification of grassland systems is leading to serious environmental risks due to the large input of nitrogen (N) in fertilizers and the subsequent gaseous losses. Addition of nitrification inhibitors (NI) or urease activity inhibitors to fertilizers could reduce these losses to the atmosphere. In the present study, the effects of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) and the urease activity inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) were evaluated on NH3, N2O, NO, and CO2 emissions. Ammonium sulphate nitrate (ASN), urea and cattle slurry were applied at a rate of 70 kg N ha(-1) to a mixed clover-ryegrass sward in the Basque Country (northern Spain) under different soil water contents. NH3 and NO emissions were determined by photoacoustic and chemiluminescence respectively using an open chamber technique while N2O and CO2 emissions were measured by photoacoustic using a closed chamber technique. When the water filled pore space (WFPS) was under 60%, the application of NBPT reduced NO emissions a 34% on urea and an 18% on slurry, and the application of DMPP reduced them a 2% on ASN and a 4% on slurry. No significant effect was observed on NH3 losses. When WFPS was over 60%, no effect could be observed on NO and N2O emissions after the application of both inhibitors, but NH3 losses were reduced a 31% by NBPT when applied with the slurry. Carbon dioxide emissions were unaffected by the use of DMPP or NBPT at any soil water content. Neither grassland yield nor herbage N concentration were influenced by the application of both inhibitors.

The effect of cattle slurry electroflotation products as fertilizers on gaseous emissions and grassland yield.

The climatic conditions of the Basque Country (northern Spain) provide the favorable conditions for the growth of grasslands and the development of livestock enterprises. The intensification of the farms is leading to serious environmental risks due to the great generation of manures and slurries and their subsequent inefficient management. Their application involves N losses that can be pollutant. The environmental company ADE BIOTEC S.L. is developing the process called "electroflotation" with the aim of reducing the volume of slurries from intensive livestock farms. The process consists basically of an electrolysis of the slurry catalyzed by iron which leads to the flocculation of the solid particles, giving as a final result a solid and a liquid fraction. The objective of this work was to assess the usefulness of these two fractions as fertilizers. With this aim, the environmental risk of their application was determined regarding gaseous emissions to the atmosphere (i.e., of NO, NH(3), N(2)O, and CO(2)) and their fertilizer capacity was investigated by determining their effects on grassland yield and N uptake in comparison to the untreated slurry. The untreated slurry and the solid and the liquid fractions were all applied at a rate of 70 kg NH(4)(+)-N ha(-1). The application of the products of electroflotation did not affect N(2)O and CO(2) losses, being of the same magnitude as those caused by the application of the original slurry. However, after their application, a reduction in NH(3) volatilization losses was induced in the short term and a reduction in NO losses was caused in the long term. The solid and liquid fractions both increased biomass yield with respect to the untreated slurry. The solid fraction even induced a higher N uptake than the liquid fraction and the untreated slurry.

3,4-Dimethylpyrazol phosphate effect on nitrous oxide, nitric oxide, ammonia, and carbon dioxide emissions from grasslands.

Intensively managed grasslands are potentially a large source of NH3, N2O, and NO emissions because of the large input of nitrogen (N) in fertilizers. Addition of nitrification inhibitors (NI) to fertilizers maintains soil N in ammonium form. Consequently, N2O and NO losses are less likely to occur and the potential for N utilization is increased, and NH3 volatilization may be increased. In the present study, we evaluated the effectiveness of the nitrification inhibitor 3,4-dimethylpyrazol phosphate (DMPP) on NH3, N2O, NO, and CO2 emissions following the application of 97 kg N ha(-1) as ammonium sulfate nitrate (ASN) and 97 kg NH4+ -N ha(-1) as cattle slurry to a mixed clover-ryegrass sward in the Basque Country (northern Spain). After slurry application, 16.0 and 0.7% of the NH4+ -N applied was lost in the form of N2O and NO, respectively. The application of DMPP induced a decrease of 29 and 25% in N2O and NO emissions, respectively. After ASN application 4.6 and 2.8% of the N applied was lost as N2O and NO, respectively. The application of DMPP with ASN (as ENTEC 26; COMPO, Münster, Germany) unexpectedly did not significantly reduce N2O emissions, but induced a decrease of 44% in NO emissions. The amount of NH4+ -N lost in the form of NH3 following slurry and slurry + DMPP applications was 7.8 and 11.0%, respectively, the increase induced by DMPP not being statistically significant. Levels of CO2 emissions were unaffected in all cases by the use of DMPP. We conclude that DMPP is an efficient nitrification inhibitor to be used to reduce N2O and NO emissions from grasslands.