Abstract
BackgroundNatural and managed soils have been identified as the largest sources of atmospheric nitrous oxide (N2O). However, the quantification of N2O emissions from soils under natural vegetation in China and their possible responses to changing climate and atmospheric nitrogen deposition remains uncertain. In particular, information regarding N2O emissions from Chinese shrublands is lacking.MethodThis study used 28 sets of N2O field measurements in China to validate a process-based dynamic nitrogen cycle model (DyN-LPJ), which was then used to investigate the N2O fluxes from soils under natural vegetation in China from 1970 to 2009.ResultsN2O emissions from Chinese forests, grasslands, and shrublands in the 2000s were estimated to be 0.10 ± 0.06 Tg N yr.−1, 0.09 ± 0.09, Tg N yr.−1 and 0.14 ± 0.07 Tg N yr.−1, respectively. Monthly N2O fluxes were linearly correlated with precipitation, and exponentially (Q10 = 3) with air temperature. The total N2O fluxes from natural terrestrial ecosystems in China increased from 0.28 ± 0.03 Tg N yr.−1 in the 1970s to 0.46 ± 0.03 Tg N yr.−1 in the 2000s. Warming and atmospheric nitrogen deposition accounted for 37% (or 0.07 ± 0.03 Tg N) and 63% (0.11 ± 0.01 Tg N) of this increase respectively.ConclusionsOur results indicate that when compared to grassland ecosystems, N2O emissions from forest and shrubland ecosystems contain larger uncertainties due to either their uncertain areal extent or their emission rates. Long-term and continuous field measurements should be conducted to obtain more representative data in order to better constrain shrubland N2O emissions.
Highlights
Nitrous oxide (N2O) is a potent long-lived greenhouse gas with a global warming potential that is nearly 300 times greater than that of carbon dioxide (CO2), and is a major contributor to stratospheric ozone destruction (Wuebbles 2009)
Our results indicate that when compared to grassland ecosystems, N2O emissions from forest and shrubland ecosystems contain larger uncertainties due to either their uncertain areal extent or their emission rates
When we aggregated the fluxes for different ecosystems according to their specific distribution maps (Fig. S1), we found that N2O emissions from shrubland played an important role either in temperate or in subtropical regions, because of their relatively larger distribution area when compared to forest and grassland (Fig. S4, Table 2)
Summary
Nitrous oxide (N2O) is a potent long-lived greenhouse gas with a global warming potential that is nearly 300 times greater than that of carbon dioxide (CO2), and is a major contributor to stratospheric ozone destruction (Wuebbles 2009). After calibrating against the site scale observations (Gu et al 2009), we estimated an average background N2O emission from cropland of 0.13 ± 0.08 Tg N (Fig. 7, Table 3), with an average flux rate of 0.79 ± 0.47 kg N ha−1 yr.−1 for the period 2000 to 2009 This result falls within the uncertainty range of 0.72–1.66 kg N ha−1 yr.−1 reported by previous studies (Li et al 2001; Gu et al 2009) and is close to the IPCC default value of 1 kg N ha−1 yr.−1 (Lu et al 2006)
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