Abstract
The Hindu Kush Himalayan (HKH) region is one of the most ecologically vulnerable regions in the world. Several studies have been conducted on the dynamic changes of grassland in the HKH region, but few have considered grassland net ecosystem productivity (NEP). In this study, we quantitatively analyzed the temporal and spatial changes of NEP magnitude and the influence of climate factors on the HKH region from 2001 to 2018. The NEP magnitude was obtained by calculating the difference between the net primary production (NPP) estimated by the Carnegie–Ames Stanford Approach (CASA) model and the heterotrophic respiration (Rh) estimated by the geostatistical model. The results showed that the grassland ecosystem in the HKH region exhibited weak net carbon uptake with NEP values of 42.03 gC∙m−2∙yr−1, and the total net carbon sequestration was 0.077 Pg C. The distribution of NEP gradually increased from west to east, and in the Qinghai–Tibet Plateau, it gradually increased from northwest to southeast. The grassland carbon sources and sinks differed at different altitudes. The grassland was a carbon sink at 3000–5000 m, while grasslands below 3000 m and above 5000 m were carbon sources. Grassland NEP exhibited the strongest correlation with precipitation, and it had a lagging effect on precipitation. The correlation between NEP and the precipitation of the previous year was stronger than that of the current year. NEP was negatively correlated with temperature but not with solar radiation. The study of the temporal and spatial dynamics of NEP in the HKH region can provide a theoretical basis to help herders balance grazing and forage.
Highlights
Grasslands occupy approximately 40% of the world’s continental area and contribute approximately 30% to global carbon fixation [1,2,3]
We compared the monthly net primary production (NPP) estimated by the Carnegie–Ames Stanford Approach (CASA) model with the monthly
For all sites (Table 2), the NPP measured at the site and estimated by the model through cross-validation had a regression coefficient of 0.74 and root mean square error (RMSE) of 25.65 gC·m−2 (Figure 2), which indicated a high precision of the CASA model estimation
Summary
Grasslands occupy approximately 40% of the world’s continental area and contribute approximately 30% to global carbon fixation [1,2,3]. Grasslands are indispensable members of the global terrestrial carbon cycle. Grasping the carbon budget of grassland ecosystems can promote understanding of the service functions provided by grasslands and potential response to the climate system [4], and this information can help achieve the goal of sustainable and rational use of grassland resources. Most of the fluctuations in these carbon sources and sinks are caused by dramatic changes in climate [2]. Climate fluctuations usually limit the growth of grasslands and are the main cause of interannual changes in carbon sinks because they greatly reduce
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