Quantification of N2O fluxes from soil–plant systems may be biased by the applied gas chromatograph methodology
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With regard to measuring nitrous oxide (N2O) emissions from biological sources, there are three most widely adopted methods that use gas chromatograph with an electron capture detector (GC–ECD). They use: (a) nitrogen (N2) as the carrier gas (DN); (b) ascarite as a carbon dioxide (CO2) trap with DN (DN-Ascarite); and (c) a mixture gas of argon and methane as the carrier (AM). Additional methods that use either a mixture of argon and methane (or of CO2 and N2) as a make-up gas with the carrier nitrogen or soda lime (or ascarite) as a CO2 trap with the carrier helium have also been adopted in a few studies. To test the hypothesis that the use of DN sometimes considerably biases measurements of N2O emissions from plants, soils or soil–plant systems, experiments were conducted involving DN, AM and DN-Ascarite. When using DN, a significant relationship appeared between CO2 concentrations and the apparent N2O concentrations in air samples. The use of DN led to significantly overestimated N2O emissions from detached fresh plants in static chamber enclosures. Meanwhile, comparably lower emissions were found when using either the DN-Ascarite or AM methods. When an N2O flux (from a soil or a soil–plant system), measured by DN in combination with sampling from the enclosure of a static opaque chamber, was greater than 200 μg N m−2 h−1, no significant difference was found between DN and DN-Ascarite. When the DN-measured fluxes were within the ranges of <−30, −30–0, 0–30, 30–100 and 100–200 μg N m−2 h−1, significant differences that amounted to −72, −22, 5, 38 and 64 μg N m−2 h−1, respectively, appeared in comparison to DN-Ascarite. As a result, the DN measurements in rice–wheat and vegetable fields overestimated both annual total N2O emissions (by 7–62%, p < 0.05) and direct emission factors for applied nitrogen (by 6–65%). These results suggest the necessity of reassessing the available data determined from DN measurements before they are applied to inventory estimation. Further studies are required to explore appropriate approaches for the necessary reassessment. Our results also imply that the DN method should not be adopted for measuring N2O emissions from weak sources (e.g., with intensities less than 200 μg N m−2 h−1). In addition, we especially do not recommend the use of DN to simultaneously measure N2O and CO2 with the same ECD.
KeywordsNitrous oxide Emissions Gas chromatography Carrier gas Soil Plant Inventory
Gas chromatograph equipped with an electron capture detector.
A GC–ECD method that uses pure N2 alone as the carrier gas but does not introduce a high-concentration make-up gas with an electronegative group/atom or with an ionization potential lower than that of N2 (such as carbon dioxide or methane) into the detector while allowing carbon dioxide (CO2) in the air samples to enter the detector.
Different from the DN method only in that an ascarite (a type of sodium-hydroxide-coated silica) filter column is connected to the beginning of the separation column. As a result of this ascarite filter, CO2 and water vapor in the air samples cannot enter the detector.
A GC–ECD method that uses an argon–methane mixture instead of pure N2 as the carrier gas while having the same GC configuration as the DN method.
A GC–ECD method that uses N2 as the carrier gas and directly introduces a mixture of methane and argon (5–10% CH4 in Ar) into the detector as a make-up gas.
A GC–ECD method that uses N2 as the carrier gas and directly introduces a mixture of CO2 and N2 into the detector as a make-up gas.
A GC–ECD method that uses He as the carrier gas, along with an ascarite (or soda lime) filter column connected to the beginning of the separation column.
This study was jointly supported by the National Natural Science Foundation of China, the Chinese Academy of Sciences, and the European Union (grant numbers: 40425010, 40331014, KZCX2-yw-204, KZCX3-SW-440, NitroEurope IP 017841). We sincerely thank Mr. Guangren Liu, Prof. Wen Zhang, Dr. Zaixing Zhou, Dr. Shenghui Han, Mr. Gang Liu, Prof. Yong Han, Mr. Huajun Tong, Ms. Rui Wang, Mr. Jia Deng and Mr. Zhisheng Yao for their substantial assistance.
- Chen GX, Shang SH, Yu KW, Yu AD, Wu J, Wang YJ (1990) Investigation on the emission of N2O by plant. Chinese J Appl Ecol 1:94–96 (in Chinese)Google Scholar
- Chen GX, Huang GH, Shang SH, Li N, Wu J, Yu KW, Xu H, Wang YJ, Li L (1992) Measurement of N2O emission from soil, plants and soil–plant systems. In Ghazi A (ed) Proceedings of CEC and P. R. China workshop of contribution to global change. Biosphere atmosphere interactions. Brussels Belgium pp 109–114Google Scholar
- Chen X, Shen SM, Zhang L, Wu J, Wang XQ (1995) A preliminary research on the effect of nitrogen and phosphorus supply on N2O emission by crops. Chinese J Appl Ecol 6:104–105 (in Chinese)Google Scholar
- Chen GX, Xu H, Zhang Y, Zhang XJ, Li Y, Shi RJ, Yu KW, Zhang XD (2003) Plant: a potential source of the atmospheric N2O. Quaternary Sci 23:504–511 (in Chinese)Google Scholar
- Huang GH, Chen GX, Xu H (1992) Investigation on emission of nitrous oxide by aseptic soybean plant. J Integr Plant Biol (former Acta Botanica Sinica) 34:835–839 (in Chinese)Google Scholar
- IPCC (2006) Guidelines for national greenhouse gas inventories. IGES, HayamaGoogle Scholar
- IPCC (2007) In: Solomon S, Qin D, Manning M, Chen Z, Marquis M, Averyt KB, Tignor M, Miller HL (eds) Climate change 2007: the physical science basis, contribution of working group I to the fourth assessment report of the intergovernmental panel on climate change. Cambridge University Press, CambridgeGoogle Scholar
- Li N, Chen GX (1993) N2O emission by plants and influence of fertilization. Chinese J Appl Ecol 4:295–298 (in Chinese)Google Scholar
- Li YY, Yang Y, Zhang XD, Chen GX (2004) Effects of illumination, carbon source and reducing power on N2O emission from maize and soybean seedlings. Chinese J Appl Ecol 15:1851–1854 (In Chinese)Google Scholar
- Loftfield NS, Brumme R, Beese F (1992) Automated monitoring of nitrous oxide and carbon dioxide fluxes from forest soils. Soil Sci Soc Am J 56:1147–1150Google Scholar
- Mosier AR, Mack L (1980) Gas chromatographic system for precise, rapid analysis of nitrous oxide. Soil Sci Soc Am J 44:1121–1123Google Scholar
- Stearns SD, Wentworth WE (1996) Gas sampling apparatus including a sealed chamber cooperative with a separate detector chamber. US Patent: 5,528,150Google Scholar
- van Bochove E, Prévost D, Pelletier F (2000) Effects of freeze–thaw and soil structure on nitrous oxide produced in a clay soil. Soil Sci Soc Am J 64:1638–1643Google Scholar
- Zhang XJ (2001) N2O emission by tree and soil in a forest ecosystem. Ph.D. thesis of the Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, pp. 77–96, (in Chinese)Google Scholar
- Zhang XJ, Chen GX, Xu H (2002a) N2O emission from trees under different light radiances. Chinese J Appl Ecol 13:1563–1565 (in Chinese)Google Scholar
- Zhang XJ, Xu H, Chen GX (2002b) N2O emission rate from trees. ACTA Phytoecol Sin 26:538–543 (in Chinese)Google Scholar