Nitrogen and phosphorus constrain the CO2 fertilization of global plant biomass

Authors: TERRER, C - Stanford University; FRANKLIN, O - International Institute For Applied Systems Analysis; PRENTICE, I - Imperial College; KEENAN, T - University Of California; KAISER, C - University Of Vienna; VICCA, S - University Of Antwerp; FISHER, J - California Institute Of Technology; REICH, P - University Of Minnesota; STOCKER, B - Centre De Recerca Ecologia; Blumenthal, Dana

Submitted to: Nature Climate Change
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/20/2020
Publication Date: 9/1/2019
Citation: Terrer, C., Franklin, O., Prentice, I.C., Keenan, T.F., Kaiser, C., Vicca, S., Fisher, J.B., Reich, P.B., Stocker, B.D., Blumenthal, D.M. 2019. Nitrogen and phosphorus constrain the CO2 fertilization of global plant biomass. Nature Climate Change. 9:684-689. https://doi.org/10.1038/s41558-019-0545-2.
DOI: https://doi.org/10.1038/s41558-019-0545-2

Interpretive Summary: There is strong evidence that the human-induced rise in atmospheric CO2 has been stimulating photosynthesis, and is responsible for the observed long-term global increase in terrestrial carbon storage. However, evidence at the ecosystem-scale is more variable, with some CO2-manipulation experiments showing minimal increases in biomass owing to resource limitations. Here, we use meta-analysis, statistical modeling and spatial data to quantify the global magnitude and distribution of the CO2 effect on plant biomass. We find the strength of CO2 fertilization to be driven jointly by nitrogen and precipitation in ~65% of vegetated land, and phosphorus and precipitation in ~35% of vegetated land, with the N- or P-limitation modulated by the types of mycorrhizal fungi with which dominant plants associate. We estimate that end-of-century CO2 levels with warming of 2ºC will enhance aboveground biomass by 12±4% above current values, equivalent to a carbon gain of 42±12 petagrams. This research reconciles conflicting findings of the CO2 fertilisation effect across scales, and provides empirical bottom-up constraints for Earth System Models.

Technical Abstract: There is strong evidence that the human-induced rise in atmospheric CO2 has been stimulating photosynthesis, and is responsible for the observed long-term global increase in terrestrial carbon (C) storage. However, evidence at the ecosystem-scale is more variable, with some CO2-manipulation experiments showing minimal increases in biomass owing to resource limitations. The extent of these limitations on CO2 fertilization has not been quantified at the global scale, precluding an observationally-based constraint on climate projections. Here, we combine a meta-analysis of 109 grassland, shrubland, cropland and forest CO2 experiments with statistical modeling and spatial data to quantify the global magnitude and distribution of the CO2 effect on biomass. We find the strength of CO2 fertilization to be driven jointly by nitrogen (N) and precipitation in ~65% of vegetated land, and phosphorus (P) and precipitation in ~35% of vegetated land, with the N- or P-limitation modulated by mycorrhizal type. We estimate that end-of-century CO2 levels consistent with current pledges to limit future warming to 2ºC will enhance aboveground biomass by 12±4% above current values, equivalent to a carbon gain of 42±12 petagrams. The pattern of ecosystem-level responses found in experiments resembles the spatial distribution of CO2-induced changes in greenness across the globe. This research reconciles conflicting findings of the CO2 fertilisation effect across scales, and provides empirical bottom-up constraints for Earth System Models.