From: University of California - San Diego
Published September 11, 2017 05:41 PM

Rising CO2 Leading to Changes in Land Plant Photosynthesis

Researchers led by Scripps Institution of Oceanography at the University of California San Diego have determined that major changes in plant behavior have occurred over the past 40 years, using measurements of subtle changes in the carbon dioxide (CO2) currently found in the atmosphere.

The two main isotopes, or atomic forms, of carbon are carbon-12 (12C) and carbon-13 (13C). As CO2 has risen since the late 19th century, the ratio of 13C to 12C in atmospheric CO2 has decreased. That’s in part because the CO2 produced by the combustion of fossil fuels has a low 13C/12C ratio. There are other factors in nature as well, however, that have influenced the rate of decrease in the isotopic ratio.  The measured rate of decrease in the isotopic ratio turns out to be different than what scientists previously expected.

The Scripps-led team updated the record of CO2 isotopic ratios that has been made at Scripps since 1978 using air samples collected at Hawaii’s Mauna Loa and the South Pole. The researchers confirmed that the discrepancy exists and considered several reasons for it. They concluded that no combination of factors could plausibly explain the changes in the CO2 isotopic ratio unless plant behavior was changing in a way that influences how much water plants need for growth.

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