Conversion of the Nitrate Nitrogen and Nitrogen Dioxide to Nitrous Oxides in Plants

Abstract

Tobacco and wheat are known to emit nitrous oxide (N 2 O). Provided that N 2 O is a greenhouse gas about 300 times worse than carbon dioxide in its potential for global warming, it is an intriguing and important subject, whether this activity is commonly present in other plants. In this study, 17 plant taxa that had been cultured aseptically were fed with 15 N-labelled nitrate for one week (feeding period). The plant taxa were then transferred to a medium with non-labelled nitrate in gas-sealed pots and cultured for another week (emission period). The amount of labelled N 2 O emitted from the plants during the emission period was determined. This value reflects only a part of the capability of plants to convert nitrate to N 2 O, because the amount of N 2 O determined here does not correspond to the total N 2 O emission from plants, but to only an 15 N-labelled N 2 O fraction emitted during the emission period from nitrate taken up into the plants during the feeding period. It was discovered that all of the 17 plant taxa analysed, except for Eucalyptus viminalis, showed emission of 15 N 2 O. The emission ranged from 0.45 ± 0.20 ng N 2 O/g fresh weight (kenaf) to -0.012 ± 0.12 ng N 2 O/g fresh weight (Eucalyptus viminalis). This activity of converting nitrate to N 2 O is obviously common in plants with some exceptions. There was more than a 58-fold variation between the highest (Hibiscus cannabinus) and the second lowest (Nicotiana tabacum) capability to convert nitrate to N 2 O among the 17 plant taxa. The present result indicates that the potential of plants to convert nitrate to N 2 O highly varies among the plant species as in the case of the assimilation of nitrogen dioxide (N 2 O) where more than a 600-fold variation was observed among 217 plant taxa. A negative correlation was obtained for N 2 O emission and NO 2 assimilation (r = 0.72).This is the first report where there was a competitive interaction between the assimilation and dissimilation activities in plants. It was also found that wild type and transgenic tobacco are able to convert NO 2 to N 2 O when they were fumigated with 15 N-labelled NO 2 . However since the N 2 O emission values observed in this study were approximately three orders of magnitude smaller than those observed with wheat leaves, the evaluation of the environmental significance of the N 2 O emission by plants must await quantitative analysis using the present system to figure out the full N 2 O emission capability of plants.

Contribution of plants to N 2 O emissions in soil-winter wheat ecosystem: pot and field experiments

“…The correlation between N 2 O emissions from plants (N 2 O E ) and plant respiratory coefficient (R E ) in this study indicated that N 2 O emissions from plants might be associated with plant respiration. Hakata et al (2003) also found that there was more than a 58-fold variation in the 'N 2 O Emission' in the 17 plant taxa, which suggested plants N 2 O emissions might be involved with plant intrinsic physiological characteristics. On the other hand, night-time plant transpiration appears to be potentially widespread in plants.…”

“…The result obtained by Smart and Bloom (2001) demonstrated that wheat leaves emit N 2 O during nitrate assimilation. A study with 17 plant taxa indicated that plant N 2 O emission was common in plant tissues (Hakata et al, 2003).…”

Enhanced UV-B radiation reduced soil-soybean ecosystem respiration and nitrous oxide emissions

“…Second, UV-B radiation may lower plant N 2 O production. It is extensively reported that soybean crops can produce and release part of N 2 O for the physiological reaction of plant tissues (Li et al 2003;Hakata et al 2003;Rochette et al 2004). Soybean crops can produce and release part of N 2 O, which is strongly positively correlated with the content of nitrate and activity of foliar nitrate reductase (NR) (Li et al 2003).…”

Quantification of N2O fluxes from soil–plant systems may be biased by the applied gas chromatograph methodology

“…Since the early report that detached fresh soybean organs may produce N 2 O (Chen et al, 1990), a number of studies have reported N 2 O emissions from plants (e.g., Chen et al 1992Chen et al , 2002Hakata et al 2003;Huang et al 1992;Li and Chen 1993;Zhang 2001;Zhang et al 2002a, b) and have indicated a considerable contribution of plant emissions to the N 2 O release from soil-plant systems (e.g., Chen et al 2003;Pihlatie et al 2005;Smart and Bloom 2001;Xu et al 2001;Zou et al 2005). In a considerable portion of these studies, the DN method was used in GCECDs to analyze air samples collected from chamber enclosures.…”

“…In addition, living plants also release N 2 O (e.g., Chen et al 1990;Smart and Bloom 2001). To quantify the intensities from these sources, N 2 O emission measurements from natural and managed soils, soil-plant systems (e.g., Stehfest and Bouwman 2006) and plants (e.g., Hakata et al 2003;Pihlatie et al 2005;Zou et al 2005) have been carried out worldwide. Global estimates of 1.7-4.8 and 3.3-9.0×10 12 g N 2 O-N yr −1 for agricultural terrain and soils under natural vegetation, respectively, have been given (IPCC 2007).…”