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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2020-26
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-26
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 28 Feb 2020

Submitted as: research article | 28 Feb 2020

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This preprint is currently under review for the journal BG.

Spatially asynchronous changes in strength and stability of terrestrial net ecosystem productivity

Erqian Cui1,2, Chenyu Bian1,2, Yiqi Luo3, Shuli Niu4,5, Yingping Wang6, and Jianyang Xia1,2 Erqian Cui et al.
  • 1Zhejiang Tiantong Forest Ecosystem National Observation and Research Station, Shanghai Key Lab for Urban Ecological Processes and Eco-Restoration, School of Ecological and Environmental Sciences, East China Normal University, Shanghai 200241, China
  • 2Research Center for Global Change and Ecological Forecasting, East China Normal University, Shanghai 200241, China
  • 3Center for ecosystem science and society, Northern Arizona University, Arizona, Flagstaff, AZ 86011, USA
  • 4Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, China
  • 5University of Chinese Academy of Sciences, Beijing, China
  • 6CSIRO Oceans and Atmosphere, PMB 1, Aspendale, Victoria 3195, Australia

Abstract. Multiple lines of evidence have demonstrated the persistence of global land carbon (C) sink during the past several decades. However, both annual net ecosystem productivity (NEP) and its inter-annual variation (IAVNEP) keep varying over space. Thus, identifying local indicators for the spatially varying NEP and IAVNEP is critical for locating the major and sustainable C sinks on the land. Here, based on a machine-learning-derived database, we first showed that the variations of NEP and IAVNEP are spatially asynchronous. Then, based on daily NEP observations from eddy covariance sites, we found robust logarithmic correlation between annual NEP and ratio of total CO2 exchanges during net uptake (U) and release (R) periods (i.e., U/R). The cross-site variation of mean annual NEP can be linearly indicated by ln(U/R), while the spatial distribution of IAVNEP was well indicated by the slope (i.e., β) of the demonstrated logarithmic correlation. Among biomes, for example, forests and croplands had the largest U/R ratio (1.06 ± 0.83) and β (473 ± 112 g C m−2 yr−1), indicating the highest NEP and IAVNEP in forests and croplands, respectively. We further showed that the spatial variations of NEP and IAVNEP were both underestimated by the machine-learning-based and process-based global models. Overall, this study underscores the asynchronously changes in the strength and stability of land C sinks over space, and provides two simple local indicators for their intricate spatial variations. These indicators could be helpful for locating the persistent terrestrial C sinks and provides valuable constraints for improving the simulation of land-atmospheric C exchanges.

Erqian Cui et al.

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Erqian Cui et al.

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Short summary
Mean annual NEP is related to the magnitude of carbon sink of a specific ecosystem, while IAVNEP characterizes the stability of such carbon sink. Thus, a better understanding of the co-varying NEP and IAVNEP is critical for locating the major and stable carbon sinks on the land. Based on daily NEP observations from eddy covariance sites, we found local indicators for the spatially varying NEP and IAVNEP, respectively.
Mean annual NEP is related to the magnitude of carbon sink of a specific ecosystem, while IAVNEP...
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