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Title: Atmospheric evidence for a global secular increase in carbon isotopic discrimination of land photosynthesis

Abstract

First, a decrease in the 13C/12C ratio of atmospheric CO2 has been documented by direct observations since 1978 and from ice core measurements since the industrial revolution. This decrease, known as the 13C-Suess effect, is driven primarily by the input of fossil fuel-derived CO2 but is also sensitive to land and ocean carbon cycling and uptake. Using updated records, we show that no plausible combination of sources and sinks of CO2 from fossil fuel, land, and oceans can explain the observed 13C-Suess effect unless an increase has occurred in the 13C/12C isotopic discrimination of land photosynthesis. A trend toward greater discrimination under higher CO2 levels is broadly consistent with tree ring studies over the past century, with field and chamber experiments, and with geological records of C3 plants at times of altered atmospheric CO2, but increasing discrimination has not previously been included in studies of long-term atmospheric 13C/12C measurements. In our paper, we further show that the inferred discrimination increase of 0.014 ± 0.007‰ ppm-1 is largely explained by photorespiratory and mesophyll effects. This result implies that, at the global scale, land plants have regulated their stomatal conductance so as to allow the CO2 partial pressure within stomatal cavities andmore » their intrinsic water use efficiency to increase in nearly constant proportion to the rise in atmospheric CO2 concentration.« less

Authors:
ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [3];  [1];  [1];  [1];  [4];  [1];  [5]
  1. Univ. of California, San Diego, CA (United States). Scripps Inst. of Oceanography
  2. Imperial College London, London (United Kingdom). Dept. of Physics and Grantham Inst.
  3. Purdue Univ., West Lafayette, IN (United States). Earth, Atmospheric, and Planetary Sciences
  4. Cornell Univ., Ithaca, NY (United States). School of Integrative Plant Science
  5. Univ. of Groningen, Groningen (The Netherlands). Center for Isotope Research
Publication Date:
Research Org.:
Univ. of California, San Diego, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1535353
Grant/Contract Number:  
SC0012167
Resource Type:
Accepted Manuscript
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 114; Journal Issue: 39; Journal ID: ISSN 0027-8424
Publisher:
National Academy of Sciences
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; science & technology; carbon cycle; photosynthesis; isotope; water use efficiency; carbon-13 Suess effect

Citation Formats

Keeling, Ralph F., Graven, Heather D., Welp, Lisa R., Resplandy, Laure, Bi, Jian, Piper, Stephen C., Sun, Ying, Bollenbacher, Alane, and Meijer, Harro A. J. Atmospheric evidence for a global secular increase in carbon isotopic discrimination of land photosynthesis. United States: N. p., 2017. Web. doi:10.1073/pnas.1619240114.
Keeling, Ralph F., Graven, Heather D., Welp, Lisa R., Resplandy, Laure, Bi, Jian, Piper, Stephen C., Sun, Ying, Bollenbacher, Alane, & Meijer, Harro A. J. Atmospheric evidence for a global secular increase in carbon isotopic discrimination of land photosynthesis. United States. doi:10.1073/pnas.1619240114.
Keeling, Ralph F., Graven, Heather D., Welp, Lisa R., Resplandy, Laure, Bi, Jian, Piper, Stephen C., Sun, Ying, Bollenbacher, Alane, and Meijer, Harro A. J. Mon . "Atmospheric evidence for a global secular increase in carbon isotopic discrimination of land photosynthesis". United States. doi:10.1073/pnas.1619240114. https://www.osti.gov/servlets/purl/1535353.
@article{osti_1535353,
title = {Atmospheric evidence for a global secular increase in carbon isotopic discrimination of land photosynthesis},
author = {Keeling, Ralph F. and Graven, Heather D. and Welp, Lisa R. and Resplandy, Laure and Bi, Jian and Piper, Stephen C. and Sun, Ying and Bollenbacher, Alane and Meijer, Harro A. J.},
abstractNote = {First, a decrease in the 13C/12C ratio of atmospheric CO2 has been documented by direct observations since 1978 and from ice core measurements since the industrial revolution. This decrease, known as the 13C-Suess effect, is driven primarily by the input of fossil fuel-derived CO2 but is also sensitive to land and ocean carbon cycling and uptake. Using updated records, we show that no plausible combination of sources and sinks of CO2 from fossil fuel, land, and oceans can explain the observed 13C-Suess effect unless an increase has occurred in the 13C/12C isotopic discrimination of land photosynthesis. A trend toward greater discrimination under higher CO2 levels is broadly consistent with tree ring studies over the past century, with field and chamber experiments, and with geological records of C3 plants at times of altered atmospheric CO2, but increasing discrimination has not previously been included in studies of long-term atmospheric 13C/12C measurements. In our paper, we further show that the inferred discrimination increase of 0.014 ± 0.007‰ ppm-1 is largely explained by photorespiratory and mesophyll effects. This result implies that, at the global scale, land plants have regulated their stomatal conductance so as to allow the CO2 partial pressure within stomatal cavities and their intrinsic water use efficiency to increase in nearly constant proportion to the rise in atmospheric CO2 concentration.},
doi = {10.1073/pnas.1619240114},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
number = 39,
volume = 114,
place = {United States},
year = {2017},
month = {9}
}

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