Abstract
Estimating the grassland carbon budget is critically important for ensuring that grassland resources are used sustainably. However, the spatiotemporal dynamics of the carbon budget and the response to grazing have not yet been characterized in Qinghai grasslands. Here, we estimated the gross primary productivity (GPP) and net ecosystem exchange (NEE) in Qinghai grasslands using the improved Biome-BGCMuSo model to characterize the spatiotemporal dynamics of the carbon budget and the response to grazing in this region from 1979 to 2018. The GPP of Qinghai grasslands fluctuated during the study period, with an average annual value of 118.78 gC/m2. The NEE of Qinghai grasslands fluctuated from 1979 to 2018, with an average value of −5.16 gC/m2. After 2,000, GPP increased, and NEE decreased in a fluctuating manner. There were clear regional differences in GPP and NEE. GPP was low in most areas of Qinghai, and GPP was high in eastern and southern Qinghai. The southern, southeastern, and northeastern parts of Qinghai were mainly carbon sinks, and the northwestern part of Qinghai and the region between the southeastern and northeastern parts of Qinghai were mainly carbon sources. Grazing generally decreased GPP and increased NEE in Qinghai grasslands from 1979 to 2018. There was spatial heterogeneity in the effect of grazing on GPP and NEE. Under grazing, GPP and NEE were significantly decreased mainly in eastern Qinghai, and GPP and NEE were significantly increased mainly in southern and eastern Qinghai. NEE was most affected by grazing in eastern Qinghai. The results of this study aid our understanding of the mechanism driving variation in the grassland carbon budget and provide new data that could be used to support local grassland management.
Highlights
Quantitative assessment of the carbon budget of terrestrial ecosystems is essential for regional carbon sink management and the implementation of action plans for climate change mitigation (Webb et al, 2019; Giltrap et al, 2020; Li et al, 2020)
The spatial distribution of the standard deviation of Gross primary productivity (GPP) was generally similar to that of the annual average GPP, which indicated that the regions with large interannual change in GPP were mainly concentrated in the regions with high absolute values of the annual averages
GPP and net ecosystem exchange (NEE) values were more strongly affected by grazing in eastern Qinghai, which was consistent with the high grass yield and high grazing intensity in this area (Figure 1B; Huang et al, 2018; Wang et al, 2019)
Summary
Quantitative assessment of the carbon budget of terrestrial ecosystems is essential for regional carbon sink management and the implementation of action plans for climate change mitigation (Webb et al, 2019; Giltrap et al, 2020; Li et al, 2020). The net ecosystem exchange (NEE) is the difference between GPP and the efflux of CO2 released back to the atmosphere through ecosystem respiration processes (Hao et al, 2020; Nascimento Alves et al, 2021). It directly reflects the carbon sink capacity of ecosystems (Yang et al, 2019). They are both key indicators of the terrestrial carbon budget. These previous studies have shown that estimates of the carbon budget can vary greatly among regions and depend on the methods used and the grassland types analyzed (Gilmanov et al, 2007; Moinet et al, 2017; Rong et al, 2017; Zhao et al, 2019; Song et al, 2020; You et al, 2020)
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