The Response of Four Woody Ecosystems to Atmospheric CO2 Enrichment

Paper Reviewed Walker, A.P., De Kauwe, M.G., Medlyn, B.E., Zaehle, S., Iversen, C.M., Asao, S., Guenet, B., Harper, A., Hickler, T., Hungate, B.A., Jain, A.K., Luo, Y., Lu, X., Lu, M., Luus, K., Megonigal, J.P., Oren, R., Ryan, E., Shu, S., Talhelm, A., Wang, Y.-P., Warren, J.M., Werner, C., Xia, J., Yang, B., Zak, D.R. and Norby, R.J. 2019. Decadal biomass increment in early secondary succession woody ecosystems is increased by CO2 enrichment. Nature Communications 10: 454, DOI: 10.1038/s41467-019-08348-1. According to Walker et al. (2019), biomass responses represent the largest component of uncertainty in Earth System model projections of terrestrial carbon sink responses to increasing CO2, where it is uncertain if CO2-induced growth enhancements observed in short-term experiments are maintained at expanded spatial and temporal scales. In searching for an answer to this important question, the 27-member research team of Walker et al. analyzed the biomass and net primary production (NPP) responses from four long-term (one decade) ecosystem CO2-enrichment experiments conducted in the United States. All of the site locations were dominated by woody plant species and each study had measured major components of NPP. And what did the analysis reveal? The percent increase in biomass due to CO2 enrichment (to 550-700 ppm) in the four early-secondary-succession temperate ecosystems was 29 ± 11.7% over the course of their operational existence (about a decade), whereas the percent change in NPP was a positive 22.9 ± 6.1% over the same period. What is more, the temporal change in biomass was found to be related to the cumulative change in NPP (cNPP) such that for every kg C m-2 increase in cNPP, the change in vegetative biomass increased by 0.55 ± 0.17 kg C m-2. The above findings represent a very positive outcome in terms of the growth and productivity of woody ecosystems in response to elevated levels of atmospheric CO2, which positive outcome will be realized in the decades to come as the air’s CO2 content continues to rise in response to humanity’s use of fossil energy. And that is great news for the terrestrial biosphere! This article appeared on the CO2 Science website at http://www.co2science.org/articles/V22/jul/a12.php]]>

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