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Light A Major Factor In Limiting Carbon Uptake
July 28, 2020

Most projections about climate change assume that, as temperatures rise, regions in the north high latitudes may become more suitable for the growth of vegetation, turning into cropland to feed increasing populations while also fixing more carbon dioxide (CO2) and slowing down climate change. Plants require appropriate temperature, water, and light conditions for photosynthesis and growth, so it seems logical that as temperatures increase in the northern high latitudes, plant photosynthesis, which uses CO2 to release oxygen, should also increase. At the same time, plant respiration, which uses oxygen to release CO2 and is also highly dependent on temperature, is expected to increase, too. The critical question still under debate is whether autumn warming might lead to an increase in carbon uptake, i.e., the difference between photosynthesis and respiration.

According to information, a new Columbia Engineering study demonstrates that even when temperatures warm and cold stress is limited, light is still a major factor in limiting carbon uptake of northern high latitudes. The team, led by Pierre Gentine, associate professor of earth and environmental engineering, analyzed satellite observations, field measurements, and model simulations and showed that there is a prevalent radiation limitation on carbon uptake in northern ecosystems, especially in autumn. Using a new dataset, Prof. Gentine’s group developed an algorithm to map global plant photosynthesis and then developed a framework to quantify the limitation of light on photosynthesis. The study, “Light limitation regulates the response of autumn terrestrial carbon uptake to warming,” was published recently in Nature Climate Change.

Prof. Gentine’s team found that, at northern latitudes that are more than 30N, the end-of-season photosynthesis response to warming is mostly dictated by light. In some of those regions in the fall, the length of daily light shortens very quickly. Less light leads to weaker photosynthesis, which in turn cannot offset the increased respiration induced by global warming. Because northern high latitudes have stronger light limitation, their vegetation will release more carbon in the fall if warming continues.

In the future, light limitation will increase as the vegetation growing season lengthens due to global warming. Earlier starts of the season in spring and later ends of the season in fall correspond to shorter day lengths and less solar radiation, posing a stronger light limit on vegetation photosynthesis.

The study was supported by NASA Advanced Information Systems Technology #NASA NNH16ZDA001N-AIST, NASA ROSES Terrestrial hydrology #NNH17ZDA00IN-THP, and #NOAA MAPP NA17OAR4310127.

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