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Nitrous oxide emissions from grass swards during the eighth year of elevated atmospheric p CO 2 (Swiss FACE)
Author(s) -
Baggs E. M.,
Richter M.,
Hartwig U. A.,
Cadisch G.
Publication year - 2003
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1046/j.1365-2486.2003.00654.x
Subject(s) - lolium perenne , trifolium repens , lolium , nitrous oxide , agronomy , zoology , fertilizer , perennial plant , carbon dioxide , chemistry , poaceae , biology , organic chemistry
Emissions of N 2 O were measured during the growth season over a year from grass swards under ambient (360 μL L −1 ) and elevated (600 μL L −1 ) CO 2 partial pressures at the Free Air Carbon dioxide Enrichment (FACE) experiment, Eschikon, Switzerland. Measurements were made following high (56 g N m −2 yr −1 ) and low (14 g N m −2 yr −1 ) rates of fertilizer application, split over 5 re‐growth periods, to Lolium perenne , Trifolium repens and mixed Lolium / Trifolium swards. Elevated p CO 2 increased annual emissions of N 2 O from the high fertilized Lolium and mixed Lolium / Trifolium swards resulting in increases in GWP (N 2 O emissions) of 179 and 111 g CO 2 equivalents m −2 , respectively, compared with the GWP of ambient p CO 2 swards, but had no significant effect on annual emissions from Trifolium monoculture swards. The greater emissions from the high fertilized elevated p CO 2 Lolium swards were attributed to greater below‐ground C allocation under elevated p CO 2 providing the energy for denitrification in the presence of excess mineral N. An annual emission of 959 mg N 2 O‐N m −2 yr −1 (1.7% of fertilizer N applied) was measured from the high fertilized Lolium sward under elevated p CO 2 . The magnitude of emissions varied throughout the year with 84% of the total emission from the elevated p CO 2 Lolium swards measured during the first two re‐growths (April–June 2001). This was associated with higher rainfall and soil water contents at this time of year. Trends in emissions varied between the first two re‐growths (April–June 2001) and the third, fourth and fifth re‐growths (late June–October 2000), with available soil NO 3 − and rainfall explaining 70%, and soil water content explaining 72% of the variability in N 2 O in these periods, respectively. Caution is therefore required when extrapolating from short‐term measurements to predict long‐term responses to global climate change. Our findings are of global significance as increases in atmospheric concentrations of CO 2 may, depending on sward composition and fertilizer management, increase greenhouse gas emissions of N 2 O, thereby exacerbating the forcing effect of elevated CO 2 on global climate. Our results suggest that when applying high rates of N fertilizer to grassland systems, Trifolium repens swards, or a greater component of Trifolium in mixed swards, may minimize the negative effect of continued increasing atmospheric CO 2 concentrations on global warming.