The fate of carbon in a mature forest under carbon dioxide enrichment

• Published in: Nature (London) Vol. 580; no. 7802; pp. 227 - 231
• Main Authors: Jiang, Mingkai, Medlyn, Belinda E., Drake, John E., Duursma, Remko A., Anderson, Ian C., Barton, Craig V. M., Boer, Matthias M., Carrillo, Yolima, Castañeda-Gómez, Laura, Collins, Luke, Crous, Kristine Y., De Kauwe, Martin G., dos Santos, Bruna M., Emmerson, Kathryn M., Facey, Sarah L., Gherlenda, Andrew N., Gimeno, Teresa E., Hasegawa, Shun, Johnson, Scott N., Kännaste, Astrid, Macdonald, Catriona A., Mahmud, Kashif, Moore, Ben D., Nazaries, Loïc, Neilson, Elizabeth H. J., Nielsen, Uffe N., Niinemets, Ülo, Noh, Nam Jin, Ochoa-Hueso, Raúl, Pathare, Varsha S., Pendall, Elise, Pihlblad, Johanna, Piñeiro, Juan, Powell, Jeff R., Power, Sally A., Reich, Peter B., Renchon, Alexandre A., Riegler, Markus, Rinnan, Riikka, Rymer, Paul D., Salomón, Roberto L., Singh, Brajesh K., Smith, Benjamin, Tjoelker, Mark G., Walker, Jennifer K. M., Wujeska-Klause, Agnieszka, Yang, Jinyan, Zaehle, Sönke, Ellsworth, David S.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-04-2020; Nature Publishing Group
• Subjects: 704/158/2165; 704/158/2445; 704/158/2454; 704/47/4113; Analysis; Atmosphere - chemistry; Atmospheric carbon dioxide; Australia; Biomass; Carbon budget; Carbon dioxide; Carbon Dioxide - analysis; Carbon Dioxide - metabolism; Carbon dioxide atmospheric concentrations; Carbon dioxide concentration; Carbon fixation; Carbon Sequestration; Carbon sinks; Carbon uptake; Climate change; Climate change mitigation; Climate Research; Earth and Related Environmental Sciences; Ecosystems; Enrichment; Environmental aspects; Environmental Sciences; Estimates; Eucalyptus - growth & development; Eucalyptus - metabolism; Experiments; Fertilization; Fluxes; Forecasts and trends; Forest carbon; Forest ecosystems; Forest Science; Forests; Geovetenskap och miljövetenskap; Global Warming - prevention & control; Humanities and Social Sciences; Hypotheses; Klimatforskning; Miljövetenskap; Models, Biological; multidisciplinary; Natural Sciences; Naturgeografi; Naturvetenskap; Negative feedback; New South Wales; Old growth forests; Photosynthesis; Physical Geography; Primary production; Respiration; Science; Science (multidisciplinary); Skogsvetenskap; Soil - chemistry; Soil respiration; Standard deviation; Supply and demand; Trees; Trees - growth & development; Trees - metabolism; New South Wales; Australia
• ISSN: 0028-0836; 1476-4687; 1476-4687
• DOI: 10.1038/s41586-020-2128-9

Atmospheric carbon dioxide enrichment (eCO
2
) can enhance plant carbon uptake and growth
1
–
5
, thereby providing an important negative feedback to climate change by slowing the rate of increase of the atmospheric CO
2
concentration
6
. Although evidence gathered from young aggrading forests has generally indicated a strong CO
2
fertilization effect on biomass growth
3
–
5
, it is unclear whether mature forests respond to eCO
2
in a similar way. In mature trees and forest stands
7
–
10
, photosynthetic uptake has been found to increase under eCO
2
without any apparent accompanying growth response, leaving the fate of additional carbon fixed under eCO
2
unclear
4
,
5
,
7
–
11
. Here using data from the first ecosystem-scale Free-Air CO
2
Enrichment (FACE) experiment in a mature forest, we constructed a comprehensive ecosystem carbon budget to track the fate of carbon as the forest responded to four years of eCO
2
exposure. We show that, although the eCO
2
treatment of +150 parts per million (+38 per cent) above ambient levels induced a 12 per cent (+247 grams of carbon per square metre per year) increase in carbon uptake through gross primary production, this additional carbon uptake did not lead to increased carbon sequestration at the ecosystem level. Instead, the majority of the extra carbon was emitted back into the atmosphere via several respiratory fluxes, with increased soil respiration alone accounting for half of the total uptake surplus. Our results call into question the predominant thinking that the capacity of forests to act as carbon sinks will be generally enhanced under eCO
2
, and challenge the efficacy of climate mitigation strategies that rely on ubiquitous CO
2
fertilization as a driver of increased carbon sinks in global forests.
Carbon dioxide enrichment of a mature forest resulted in the emission of the excess carbon back into the atmosphere via enhanced ecosystem respiration, suggesting that mature forests may be limited in their capacity to mitigate climate change.