## 4 Discussion  
### Comparison with Previous Studies  
The modeled NPP is comparable with reported field observations or satellites estimates. The results of this study demonstrated that the mean NPP for Central Asia in 1979-2011 was 281.79 gC m\({}^{-2}\) yr\({}^{-1}\), which is higher than the simulation of [PERSON] and [PERSON] (2016) of 218 gC m\({}^{-2}\) yr\({}^{-1}\). The cropland had the highest NPP (646.25 gC m\({}^{-2}\) yr\({}^{-1}\)) compared with the other types, which is between the range of [PERSON] and [PERSON] (2016) and [PERSON], et al. (2018). Annual NPP for forest was 277.49 gC m\({}^{-2}\) yr\({}^{-1}\), which is smaller than NPP in East China from 2001 to 2008 ([PERSON] et al., 2018). Shrubland and grassland presented the lowest NPP at approximately 112.50 gC m\({}^{-2}\) yr\({}^{-1}\) and 90.94 gC m\({}^{-2}\) yr\({}^{-1}\), respectively, which are lower than the average NPP in China, as reported by [PERSON], et al. (2018), as a result of the lower precipitation in Central Asia compared with China (Table 2).  
Grassland lost its carbon storage by \(-\)0.21 gC m\({}^{-2}\) yr\({}^{-1}\), whereas the other three types were carbon sinks. Comparison with previous studies reveal that the carbon dynamics of the present work is comparable and realistic. Greenhouse gas emissions come from various practices in the grassland ecosystem, and in this study, grazing exerted a strong impact on terrestrial carbon balance over the past 33 years, which was confirmed by [PERSON] et al. (2018). Forest and shrubland had the highest carbon sequestration potential, and numerous studies have reported that the forest ecosystems was an indispensable carbon sink in China and Asia (2016); China and Asia (2016); [PERSON] et al. (2018); [PERSON] et al. (2018). [PERSON] et al. (2018) illustrated that forest land use in Central Asia acts as a carbon sink, and accelerated deforestation leads to strong carbon sequestration. [PERSON] et al. (2018) examined how ecosystem production in one shrubland in Northern China varied during 2012-2014, and their results indicated a shift from an annual sink to a carbon source.  
Spatio-temporal patterns of carbon dynamics have been estimated in many regions around the world. Nevertheless, the arid and semi-arid regions of Central Asia were poorly analyzed and with great uncertainty. Only a few studies have been conducted in this region, but with varied limitations. [PERSON] et al. (2018) estimated carbon stocks in Central Asia without analyzing the differences between different vegetation types. [PERSON] et al. (2018) reveal the value of carbon budget in Central Asia, but only concerning the forest land use and management process. [PERSON] et al. (2018) conducted an experimental study on fencing effects in a meadow steppe in Central Asia, however, their research is limited to only a few sites. [PERSON] et al. (2018) and [PERSON] et al. (2018) examined the effects of environmental factors on soil organic carbon in Central Asia, without considering the above ground carbon dynamics. This study, focusing on the differences between the dominant vegetation types, could give guidance to stakeholders and decision makers in increasing the regional adaptive capacity to climate change.