Ammonia emissions to the atmosphere from leaves of wild plants and Hordeum vulgare treated with methionine sulphoximine

Abstract

Using field plots, three species (Mercurialis perennis L., Rubus fruticosus L., and Trientalis europaea L.) were tested for their potential to emit gaseous ammonia to the atmosphere. Canopies were misted with 5 m methionine sulphoximine (MSO) to inhibit glutamine synthetase (GS), the enzyme of ammonium assimilation. Leaf tissue NH % + concentration of control plants was 0n03-0n1 µmol g −" f. wt. Although NH % + accumulated in the leaf tissue of MSO-treated plants of all three species to similar concentrations (6-10 µmol g −" f. wt after 4 d), emissions were only detected from the leaves of M. perennis, with potential rates of 2n5 nmol m −# leaf s −" . Experiments carried out in a controlled environment confirmed this rate of emission over 9 d, during which time leaf tissue ammonium increased to 66 µmol g −" f. wt. Comparisons with Hordeum vulgare grown under the same conditions showed that tissue NH % + concentration reached a plateau of about 40 µmol g −" f. wt after 2 d. Emissions of NH $ during the 5 d of treatment reached a maximum rate of 10 nmol m −# s −" by the third day.Apoplastic pH of the plants was determined, and it is suggested that this is an important factor explaining the differences in NH $ emission between species. The higher the apoplastic pH, the greater the likelihood of loss of NH $ from sub-stomatal spaces to the atmosphere. T. europaea (non-emitter) had an apoplastic pH of 5, R. fruticosus (non-emitter) a pH of c. 5n6, whereas that of M. perennis (emitter) was c. pH 6n3. The apoplastic pH is thought to be dictated in part by the N nutrition of a species, nitrophilous species tending to have high pH. Without NO $ − fertilization, H. vulgare had an apoplastic pH of 6n8 but this increased to 7n3, 3 d after feeding with NO $ − . Short-term fumigation (2 h) of shoots of H. vulgare with 60 µg ($ 32 mg NH $ m −$ ) of labelled gaseous "&N-NH $ (in the absence of MSO) showed that a substantial proportion (60 %) of the applied label was found in the leaves, as well as in stems and roots (3 %). There was also a change in amino acid pools, with an increase in shoot amino acids and a decrease in those in the root, while tissue NH % + was very low in both shoots and roots. This provided indirect evidence that some of the applied label had been incorporated into an organic form. Following the fumigation treatment, emissions of NH $ were collected for 3 h, then c. 6n5 µg of N was recovered, of which c. 17% was "&N-labelled. Some of this label could have resulted from desorption of NH $ from leaf surfaces, but it was more likely that the remaining "%N isotope was from sub-stomatal emissions of NH $ . It is argued that non-nitrophilous plants tend to rely on mixed sources of N (NO $ − , NH % + or organic-N) and are more likely to favour root rather than shoot assimilation. Under these circumstances, their apoplastic pH is relatively low (compared with that of nitrophiles, which tend to assimilate NO $ − mainly in their shoots), and at atmospheric concentrations most wild species are likely to be ne...

Effects of different ammoniacal nitrogen sources on N-metabolism of the atmospheric bromeliad Tillandsia pohliana Mez

“…Besides being released from the soil, NH 3 can be emitted from senescing plant parts (Hanstein & Felle 1999). In addition, plants give off N-NH 3 , through the stomata, as has been observed in rice (Oryza sativa L.) (Silva & Stutte 1981), wheat (Triticum aestivum L.) (Parton et al 1988), and pea (Pisum sativum L.) (Betelsen & Jensen 1992), as well as in several wild species, such as Mercurialis perennis L., Rubus fruticosus L., and Trientalis europaea L. (Pearson et al 1998). There is strong evidence that increased N level in the atmosphere is beneficial to epiphytic plants up to a certain limit (Baxter et al 1992).…”

Uptake and utilization of atmospheric ammonia in three native Poaceae species: leaf conductances, composition of apoplastic solution and interactions with root nitrogen supply

“…Van der Eerden et al (1992) and PerezSoba et al (1995) observed a decrease in root biomass and in mycorrhizal infection of Pinus sylvestris and Pseudotsuga menziesii after NH $ exposure over several weeks. Recently Pearson et al (1998) measured a decrease in root amino acids in H. vulgare exposed to a short NH $ pulse of high concentration. The current investigation indicates that B. erectus seems to have a lower threshold for adverse NH $ effects on root physiology than B. pinnatum and A. elatius.…”

“…However, NH % + assimilation within the leaf cells releases protons (Raven, 1988), and it has been hypothesized that growth at elevated NH $ concentrations may in the long term lead to increased shoot acid load (Raven, 1988 ;Pearson & Stewart, 1993), which could also affect the apoplastic pH. Pearson et al (1998) recently suggested that apoplastic pH is an important factor that explains differences between species in their emission of NH $ to the atmosphere. Compensation points for NH $ in plant species from natural and semi-natural ecosystems have so far only been measured in a few cases.…”

Emersion Induces Nitrogen Release and Alteration of Nitrogen Metabolism in the Intertidal Genus Porphyra

“…During photorespiration, proteins in mitochondria are deaminated and the photorespiratory NH 4 + is transferred to chloroplasts where it is re-assimilated by glutamine synthetase (GS) [42]. In higher plants, the reassimilatory flux of NH 4 + during photorespiration may be 10-fold greater than primary N assimilation [43], [44]. This N release by agricultural crops was estimated in the range of 0–4.1 kg N ha −1 y −1 [45].…”