Spatiotemporal variations of carbon flux and nitrogen deposition flux linked with climate change at the centennial scale in China

The spatial and temporal variations of the vegetation carbon flux in China from 1901 to 2005 were studied using the vegetation net primary production（NPP） values from seven Earth-system models. In addition, the temporal and spatial changes in the nitrogen deposition flux in China were studied using the NH;and NO;fluxes from 1901 to 2005. The relationship between changes in the carbon flux, nitrogen flux and climate was analyzed. The results show that（1） over the past 100 years, NPP in China has shown an upward trend. The average trend coefficient is 0.88 and the NPP distribution trend is generally low in the north and high in the south, with a gradual increase from the northwest to the southeast. Temperature, precipitation and radiation are all conducive to plant growth in the direction of the gradient. The correlation coefficients between the ensemble model mean NPP and temperature, precipitation, longwave radiation and shortwave radiation are 0.88, 0.73, 0.91 and 0.67, respectively.（2） In the past 100 years, the NH;and NO;fluxes in China have shown an upward trend, with trend coefficients of 0.98 and 0.98,respectively, which pass the 99.9% confidence level of the t-test. NH;and NO;fluxes are also generally low in the north and high in the south, with a gradual increase from the northwest to the southeast in a step-like pattern.（3） The spatial distribution of the correlation coefficients between the NH;and NO;fluxes and air temperature is similar, with only slight differences in values. The spatial distribution of the correlation coefficients between the NH;and NO;fluxes and precipitation is similar in overall pattern,but the pattern is relatively complicated, with a positive-negative-positive-negative-positive pattern occurring across the monsoon region from north to south, and a negative-positive-negative-positive pattern occurring beyond the monsoon region from east to west.（4） The spatial distribution of the correlation coefficients between the NH;and NO;fluxes and NPP shows a generally consistent pattern, but the pattern is relatively uneven. The average distribution of the ensemble model mean is positive correlation in northeast China and southwest China, and alternating positive and negative correlation in other regions.