Researchers led by Scripps Institution of Oceanography have determined that rising levels of carbon dioxide have changed plant behavior worldwide, partially mitigating the effects of human-induced climate change.
The study, released Monday in the influential journal Proceedings of the National Academy of Sciences, found that over the past 40 years plants have become more efficient at photosynthesis, the process by which sunlight converts carbon dioxide and water into food.
“The increase in the efficiency of photosynthesis documented in this study has likely helped plants offset a portion of human-induced climate change by removing more CO2 from the atmosphere than they would have otherwise,” said study lead author and Scripps scientist Ralph Keeling.
Keeling is internationally renowned for compiling the Keeling Curve, the data measuring the steady increase in atmospheric CO2 at Mauna Loa, Hawaii, since 1958.
What plants appear to be doing, according to Scripps researchers, is changing their behavior to take advantage of the greater concentration of carbon dioxide.
“Optimal or near optimal behavior has been found in smaller studies on individual plants, but this paper is the first to show that it may be evident at the scale of the entire planet,” said Keeling.
“The full implications are still far from clear, however, and any benefits may be more than offset by other negative changes, such as heat waves and extreme weather, biodiversity loss, sea level rise, and so on,” he added.
The study focused on the two main isotopes of carbon. The ratio of carbon-13 to carbon-12 has risen since the late 19th century, in part because of the burning of fossil fuels. But the researchers found that changes in the ratio could only be fully explained if plant behavior was changing in a way that influences how much water plants need for growth.
CO2 influences the behavior of stomata, the microscopic holes in leaves that allow a leaf to take in CO2. These holes also allow water to evaporate from the leaf, which must be replenished by water supplied to the roots to avoid drying out. With more CO2 in the atmosphere, a plant can afford to have smaller or fewer stomata, thus allowing more photosynthesis for the same amount of water.
The research supports a long-standing hypothesis introduced by plant biologists that posits plants will achieve an optimum response to rising CO2 levels in the atmosphere.
