Spatial variations in terrestrial net ecosystem productivity and its local indicators

Cui, Erqian; Bian, Chenyu; Luo, Yiqi; Niu, Shuli; Wang, Yingping; Xia, Jianyang

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 (IAVinline-formulaNEP) keep varying over space. Thus, identifying local indicators for the spatially varying NEP and IAVinline-formulaNEP is critical for locating the major and sustainable C sinks on land. Here, based on daily NEP observations from FLUXNET sites and large-scale estimates from an atmospheric-inversion product, we found a robust logarithmic correlation between annual NEP and seasonal carbon uptake–release ratio (i.e. inline-formulaU ∕ R). The cross-site variation in mean annual NEP could be logarithmically indicated by inline-formulaU ∕ R, while the spatial distribution of IAVinline-formulaNEP was associated with the slope (i.e. inline-formulaβ) of the logarithmic correlation between annual NEP and inline-formulaU ∕ R. Among biomes, for example, forests and croplands had the largest inline-formulaU ∕ R ratio (1.06 inline-formula± 0.83) and inline-formulaβ (473 inline-formula± 112 g C minline-formula−2 yrinline-formula−1), indicating the highest NEP and IAVinline-formulaNEP in forests and croplands, respectively. We further showed that these two simple indicators could directly infer the spatial variations in NEP and IAVinline-formulaNEP in global gridded NEP products. Overall, this study provides two simple local indicators for the intricate spatial variations in the strength and stability of land C sinks. These indicators could be helpful for locating the persistent terrestrial C sinks and provide valuable constraints for improving the simulation of land–atmospheric C exchanges.

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Cui, Erqian / Bian, Chenyu / Luo, Yiqi / et al: Spatial variations in terrestrial net ecosystem productivity and its local indicators. 2020. Copernicus Publications.

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