Plants and CO2

Plants absorb carbon dioxide and exhale Oxygen. They are a major part of the global cycle. The global uptake of carbon by land plants may be up to 45 per cent more than previously thought. This is the conclusion of an international team of scientists, based on the variability of heavy oxygen atoms in the carbon dioxide of the atmosphere driven by the El Niño effect. As the oxygen atoms in carbon dioxide were converted faster than expected during the El Niño years, current estimates for the uptake of carbon by plants are probably too low. These should be corrected upwards, say the researchers in the current issue of the scientific journal NATURE. Instead of 120 petagrams of carbon, the annual global vegetation uptake probably lies between 150 and 175 petagrams of carbon. This value is a kind of gross national product for land plants and indicates how productive the biosphere of the Earth is. The reworking of this so-called global primary productivity would have significant consequences for the coupled carbon cycle-climate model used in climate research to predict future climate change.



The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth. It is one of the most important cycles of the earth and allows for carbon to be recycled and reused throughout the biosphere and all of its organisms.
It is now usually thought of as including the following major reservoirs of carbon interconnected by these major pathways of exchange:
Atmosphere
Terrestrial biosphere (plants, animals etc.),
Oceans
Geological sources
The new analysis indicated regular fluctuations between years and a connection with the El Niño phenomenon in the Pacific. Overall, El Niño years are warmer. They are also characterized by greater precipitation in South America and less intensive monsoons in Southeast Asia. The researchers found a more rapid recovery of the isotopic ratios following the El Niño events than assumed, indicating a shorter conversion time for CO2 in the terrestrial biosphere.
On the basis of these data, the authors calculate the so-called global primary productivity (GPP). They now propose correcting this in the global models from 120 to 150-175 petagrams) of carbon annually.
"Our atmosphere is a perfect blender. Changes in its levels of trace gases — such as carbon dioxide — reflect the overall release and uptake of trace gases from all sources. So if you measure the carbon exchange of a forest ecosystem, for example, you "only" get the net exchange of all the carbon taken up by the trees for photosynthesis and all the carbon released by the trees and soil ", writes Dr. Matthias Cuntz of the Helmholtz Center for Environmental Research (UFZ) in his commentary in the same issue of NATURE. The gross-exchange fluxes, such as photosynthesis, are however accessible only with difficulty. "The researchers of Lisa Welp's team assume that around 43 per cent of all CO2 molecules entering a plant are taken up by the plant. If this were only 34%, the estimate would fall to about 120 billion tons of carbon — that is, to the currently accepted value".

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