Spatial and temporal patterns of CO2 and CH4 fluxes in China's croplands in response to multifactor environmental changes

The spatial and temporal patterns of CO2 and CH4 fluxes in China's croplands were investigated and attributed to multifactor environmental changes using the agricultural module of the Dynamic Land Ecosystem Model (DLEM), a highly integrated process-based ecosystem model. During 1980-2005 modelled results indicated that China's croplands acted as a carbon sink with an average carbon sequestration rate of 33.4 TgC yr-1 (1 Tg = 1012 g). Both the highest net CO2 uptake rate and the largest CH4 emission rate were found in southeast region of China's croplands. Of primary influences were land-cover and land-use change, atmospheric CO2 and nitrogen deposition, which accounted for 76%, 42% and 17% of the total carbon sequestration in China's croplands during the study period, respectively. The total carbon losses due to elevated ozone and climate variability/change were equivalent to 27% and 9% of the total carbon sequestration, respectively. Our further analysis indicated that nitrogen fertilizer application accounted for 60% of total national carbon uptake in cropland, whereas changes in paddy field areas mainly determined the variability of CH4 emissions. Our results suggest that improving air quality by means such as reducing ozone concentration and optimizing agronomic practices can enhance carbon sequestration capacity of China's croplands.