Field-experiment constraints on the enhancement of the terrestrial carbon sink by CO2 fertilization

Y. Liu, S. Piao, T. Gasser, P. Ciais, H. Yang, H. Wang, T.F. Keenan, M. Huang, S. Wan, J. Song, K. Wang, I.A. Janssens, J. Peñuelas, C. Huntingford, X. Wang, M.A. Arain, Y. Fang, J.B. Fisher, M. Huang, D.N. Huntzinger, A. Ito, A.K. Jain, J. Mao, A.M. Michalak, C.Peng, B. Poulter, C. Schwalm, X. Shi, H. Tian, Y. Wei, N. Zeng, Q. Zhu and T. Wang


SUMMARY

Terrestrial ecosystems play an important role in sequestering carbon dioxide (CO2) from the atmosphere. Models have shown that increasing atmospheric CO2 is one of the main drivers of increased CO2 uptake by terrestrial ecosystems, but the magnitude of increased CO2 uptake varies between models. Using terrestrial ecosystem models and data from CO2 enrichment experiments, the sensitivity of terrestrial ecosystems to atmospheric CO2 for the temperate Northern Hemisphere was examined. We found that observed increases in the global carbon sequestration by terrestrial ecosystems is explained by the fertilization effect (increased rates of photosynthesis in plants as a result of increased levels of CO2 in the atmosphere). The results of this study show the utility of using CO2 enrichment experiments for constraining terrestrial carbon model’s estimate of atmospheric CO2.

 

Figure: The effect of atmospheric CO2, eCO2, on the change in the global residual terrestrial sink (the CO2 sequestered by land which is derived from subtracting atmospheric CO2 and CO2 sequestered in the ocean from anthropogenic emissions) over the past five decades. Changes in the residual terrestrial sink (excluding emissions from land-use changes) from global budget and the effect of eCO2 on the residual terrestrial sink changes from 12 terrestrial ecosystem models (shown as multi-model mean ± s.d., shaded green area) relative to 1959. The dashed lines indicate unconstrained linear regressions. The P-values indicate the statistical significance of the linear regressions.

ABSTRACT

Clarifying how increased atmospheric CO2 concentration (eCO2) contributes to accelerated land carbon sequestration remains important since this process is the largest negative feedback in the coupled carbon–climate system. Here, we constrain the sensitivity of the terrestrial carbon sink to eCO2 over the temperate Northern Hemisphere for the past five decades, using 12 terrestrial ecosystem models and data from seven CO2 enrichment experiments. This constraint uses the heuristic finding that the northern temperate carbon sink sensitivity to eCO2 is linearly related to the site-scale sensitivity across the models. The emerging data-constrained eCO2sensitivity is 0.64 ± 0.28 PgC yr−1 per hundred ppm of eCO2. Extrapolating worldwide, this northern temperate sensitivity projects the global terrestrial carbon sink to increase by 3.5 ± 1.9 PgC yr−1 for an increase in CO2 of 100 ppm. This value suggests that CO2 fertilization alone explains most of the observed increase in global land carbon sink since the 1960s. More CO2 enrichment experiments, particularly in boreal, arctic and tropical ecosystems, are required to explain further the responsible processes.


Liu,Y., S. Piao, T. Gasser, P. Ciais, H. Yang, H. Wang, T.F. Keenan, M. Huang, S. Wan, J. Song, K. Wang, I.A. Janssens, J. Peñuelas, C. Huntingford, X. Wang, M.A. Arain, Y. Fang, J.B. Fisher, M. Huang, D.N. Huntzinger, A. Ito, A.K. Jain, J. Mao, A.M. Michalak, C.Peng, B. Poulter, C. Schwalm, X. Shi, H. Tian, Y. Wei, N. Zeng, Q. Zhu, T. Wang (2019) "Field-experiment constraints on the enhancement of the terrestrial carbon sink by CO2 fertilization," Nature Geoscience, 12, 809-814, doi:10.1038/s41561-019-0436-1.