Past studies have over-estimated how much carbon plants will spew as temperatures rise.
In the daytime, plants harness sunlight to transform carbon dioxide (CO2) into sugars, giving off oxygen as waste. But when night falls, and sunlight is replaced with darkness, plants cease photosynthesis. They continue, however, to respire by breathing in oxygen, much like humans, and expelling CO2.
As it gets hotter, plants breathe harder — again, similar to humans. This has been cited as cause for concern in a warming climate, as plant respiration already accounts for an annual flux of CO2 into the atmosphere that’s six times as large as that generated by the burning of fossil fuels. Scientists have questioned whether climbing temperatures could be triggering a feedback mechanism, whereby the CO2 spewed by heat-stressed respiring plants further heat up the atmosphere.
But a study published in Nature earlier this year showed plants can actually adjust to the heat, and in doing so, curb their release of CO2.
Scientists working in two Minnesota forests measured the amount of CO2 respired by more than 1,200 trees, across 10 species, over three to five years. With the help of heating cables, the trees were exposed to a range of temperatures, simulating how the climate is forecast to change by the end of the century.
Plants grown in temperatures 3.4 degrees Celsius above ambient temperature increased their CO2 emission by only 5 percent on average — a much smaller increase than previous lab studies looking at short-term responses to temperature have documented.
The researchers found that when trees were exposed to the warmer temperatures over a long period of time, they were able to adjust, whereas a rapid heat shock was predicted to cause the same trees to pump out 23 percent more CO2 than they would at ambient temperature.
The trend of decreasing temperature sensitivity with rising heat means that the previous estimates of how much CO2 plants will add to the atmosphere as the globe warms are too high. According to another study published in Proceeding of the National Academy of Sciences, the biggest discrepancy in estimates are in the coldest regions, where plants experience more drastic heating than those in other parts of the world, but are also adjusting quickly.
"Although these results are 'good news' in the sense that the underlying physiology of plants is not going to make the warming of the planet radically worse, the problem we have created in the first place with our greenhouse gas emissions from fossil fuel burning still exists," lead author of the Nature study Peter Reich, from the University of Minnesota, said in a press release.
"So, we very much still need to cut our carbon emissions in the coming decades by enough to stop climate change."
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