Estimating N 2 O emissions from soils under natural vegetation in China

Abstract

Background: Natural and managed soils have been identified as the largest sources of atmospheric nitrous oxide (N 2 O). However, the quantification of N 2 O 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 N 2 O emissions from Chinese shrublands is lacking. Method: This study used 28 sets of N 2 O field measurements in China to validate a process-based dynamic nitrogen cycle model (DyN-LPJ), which was then used to investigate the N 2 O fluxes from soils under natural vegetation in China from 1970 to 2009. Results: N 2 O 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 N 2 O fluxes were linearly correlated with precipitation, and exponentially (Q 10 = 3) with air temperature. The total N 2 O 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. Conclusions: Our results indicate that when compared to grassland ecosystems, N 2 O 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 N 2 O emissions.