Carbon dioxide: NMR reveals photosynthetic shift

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  • Published: Jan 15, 2016
  • Author: David Bradley
  • Channels: NMR Knowledge Base
thumbnail image: Carbon dioxide: NMR reveals photosynthetic shift

Historical plants

Rising levels of the greenhouse gas carbon dioxide in the Earth's atmosphere are the focus of great concern, as we well know. Now, scientists in Sweden have demonstrated that the anthropogenic increase since the end of the Industrial Revolution may have changed photosynthetic metababolism in green plants. Fireweed (Chamerion angustifolium). Photo by Johan Gunséus

Rising levels of the greenhouse gas carbon dioxide in the Earth's atmosphere are the focus of great concern, as we well know. Now, scientists in Sweden have demonstrated that the anthropogenic increase since the end of the Industrial Revolution may have changed photosynthetic metabolism in green plants.

A team from Umeå University and the Swedish University of Agricultural Sciences has used nuclear magnetic resonance (NMR) spectroscopy along with other techniques to investigate how plants may have changed in response to anthropogenic rising carbon dioxide levels over the 20th century. This is the first study to look at the biochemical regulation of plant metabolism from historical specimens; details are reported in the journal Proceedings of the National Academy of Sciences (USA), commonly referred to as PNAS. The findings could be used to refine our models of future carbon dioxide concentration and how plant life can affect it.

PPM

Green plants take up carbon dioxide from the air and use photosynthesis to convert it into sugars, essentially. Uptake is offset by the side reaction of photorespiration. The team in Sweden has now found that rising carbon dioxide levels in the atmosphere during the 1900s from pre-Industrial level of 280 parts per million, ppm, to today's 400 ppm) has shifted the balance of photosynthesis versus photorespiration in favour of photosynthesis. They suggest that this increased photosynthesis means more carbon dioxide uptake by plants, which may well have contributed to the ability of vegetation to dampen climate change by absorbing approximately one third of the anthropogenic carbon dioxide emissions. However, photorespiration does increase with rising temperature, which in turns suggests that as the planet warms , plants will "breathe out" more carbon dioxide, implying that this metabolic shift will be ultimately be counteracted by imminent temperature rise.

C3-CO2

"Until recently, studying how plants respond to increases in carbon dioxide on the decadal to centennial timescales has relied on simulations based on short-term experiments, because methods to detect long-term metabolic changes were not available," explains principal investigator Jürgen Schleucher of Umeå. "By reconstructing past metabolic shifts in response to environmental changes, we lay the foundation for better modelling of future plant performance," he adds. The team now has data showing the effect of carbon dioxide on the level of metabolic flux in plants over several decades.

The team used Umeå's "NMR for Life" facility to compare the metabolism in century-old herbarium specimens with new plants. By looking specifically at the intramolecular isotope patterns of glucose produced by photosynthesis, the researchers could see that shifting isotope ratios correlate with changes in the metabolic carbon dioxide flux. The study investigated various C3 plants, those that collectively account for the majority of global photosynthesis and human food crops, for example sugar beet samples grown between 1890 and 2012. Plant breeding, did not play a significant part in the observed changes, the team asserts.

"We suspected that photorespiration was stealing away a portion of photosynthesis. Now we know it was leaving fingerprints," explains team member John Marshall. Due to the fundamental nature of this change, the researchers are confident that the phenomenon will have occurred in most global vegetation, including critical peat moss species across the Northern hemisphere.

"The next step with our research is to expand it to global vegetation and to extend the time horizon to tens of thousands of years," Schleucher told us. "The ultimate goals are predictions of plant biogeochemistry, i.e. will the terrestrial vegetation remain a carbon sink in the coming century? How will crop productivity develop under climate change? To establish new tools for paleo-plant-metabolism. To study plant-climate interactions including plant acclimation on time scales of glacial cycles."

Related Links

Proc Natl Acad Sci (USA) 2015, 112, 15585–15590: "Detecting long-term metabolic shifts using isotopomers: CO2-driven suppression of photorespiration in C3 plants over the 20th century."

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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