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Enhanced seasonal CO2 exchange caused by amplified plant productivity in northern ecosystems

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Science  12 Feb 2016:
Vol. 351, Issue 6274, pp. 696-699
DOI: 10.1126/science.aac4971
  • Fig. 1 Amplification of plant activity in the northern biosphere.

    (A to E) Annual time series and linear trends of mean annual air temperature (A), peak FAPAR (fraction of absorbed photosynthetic active radiation) (B), annual amplitude of GPP (gross primary production) (C), annual amplitude of NBP (net biome productivity) (D), and seasonal amplitude of atmospheric CO2 (E) at Point Barrow (BRW) and Mauna Loa (MLO). Time series in (A) and (B) are spatially averaged; in (C) and (D) they are aggregated for boreal and arctic land regions north of 41°N (fig. S12), and the 1982–2011 mean has been subtracted. Dashed lines and trend values refer to the overlapping period of LPJmL simulations and observations. P values were calculated with the Mann-Kendall trend test.

  • Fig. 2 Latitudinal gradients of trends in the seasonal CO2 amplitude and its drivers.

    (A) Simulated and observed CO2 amplitude trends with 95% confidence intervals (dashed lines) and the uncertainty distribution of site-level trend slopes (solid lines are interquartile range; dots are median values). Site-level uncertainty distributions are not shown in (B) and (C) for clarity. (B) Global effects of CO2 fertilization and climate change on the latitudinal gradient. Removing the effect of CO2 fertilization on photosynthesis reduces CO2 amplitude trends globally but has no effect on the latitudinal gradient. The latitudinal gradient disappears with a constant climate. (C) Separation of the indirect effect of changing vegetation cover and the direct effect of climate change on photosynthesis in high-latitude regions on the latitudinal gradient. The latitudinal gradient disappears both without changes in vegetation cover (i.e., climate change but no vegetation cover change) and without climate change (i.e., forcing changes in vegetated area but no climate change).

  • Fig. 3 Trend in the CO2 amplitude at Point Barrow against trends in northern ecosystem gross primary production across different factorial model experiments with LPJmL.

    Dots and error bars represent median values and 95% confidence intervals of the estimated trends. Gray horizontal solid and dashed lines show the median and 95% confidence interval for the estimated trend in the observed CO2 amplitude time series.

Supplementary Materials

  • Enhanced seasonal CO2 exchange caused by amplified plant productivity in northern ecosystems

    Matthias Forkel, Nuno Carvalhais, Christian Rödenbeck, Ralph Keeling, Martin Heimann, Kirsten Thonicke, Sönke Zaehle, Markus Reichstein

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Materials and Methods
    • Supplementary Text
    • Figs. S1 to S13
    • Tables S1 to S7
    • References

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