Spatial variation of carbon turnover time and carbon uptake in a Chinese desert steppe ecosystem

Quantifying the carbon dynamics in arid and semi-arid ecosystems is a key issue in determining the global carbon budget. Carbon turnover time (CTT) and carbon uptake are the key indicators that determine the C dynamics and the potential C sequestration, but it has not been well quantified in a specific ecosystem. Our study combined a field inventory in a desert steppe ecosystem with data synthesis and the Terrestrial Ecosystem Regional model (TECO-R) for desert steppes to invert the key parameters of the ecosystem's carbon cycle. The average CTT in the leaf, root, and soil carbon pools (to a depth of 50 cm) and for the whole ecosystem was 1.43, 10.1, 76.96, and 37.65 years, respectively. The study area's net primary productivity (NPP) averaged 131.93 g C M-2 yr(-1) from 2000 to 2018 based on the Carnegie-Ames-Stanford approach, and the ecosystem C uptake averaged 28.86 g C M-2 yr(-1), driven by an increasing NPP trend. The whole-ecosystem CTT (CTTE) increased significantly, by about 6 years per 25-mm increase in precipitation, 0.45 degrees increase in latitude, 1000-g increase in SOC, and 50-g C m(-2) yr(-1) increase in NPP. The threshold temperature for CTT in the desert steppe was around 6 degrees C. CTTE was significantly negatively correlated with temperature above this temperature, but below this value is the opposite. However, the pattern of ecosystem potential C uptake was affected by climate, NPP, and the intensity of human activities, with no clearly dominant factor. These analyses of the desert steppe's carbon cycle will help to improve the assessment of dryland carbon dynamics and global carbon budgets.