Plants have 34% less breathing pores due to 150 years of rising CO2

According to new research by Utrecht University in the Netherlands that will be published in two separate papers in the upcoming edition of PNAS, plants react strongly to rising CO2 levels. This may in turn have strong climate implications, as the plants release less water to the atmosphere.

Comparing living plants with peat samples and herbarium collections, the researchers conclude the increase of atmospheric CO2 concentrations from preindustrial levels to the current 390 ppm, has led plants to lose one third of their stromata, or breathing pores, surface, due to a decline in number and size.

Further CO2 increase

In the second publication, also to be printed in the next edition of PNAS, the same research group presents model results showing a further doubling of CO2 concentrations to 800 ppm would further decrease breathing pores and halve the amount of water emitted to the air, thereby disturbing hydrological cycles.

Water cycle

Water is to ecology what money is to economy. It is not so much the amount that matters to create value, but the speed with which it is cycled. The researchers therefore fear that further rises in CO2 accompanied with declines in plant evaporation could lead to rainfall disturbances and droughts. Previous research last year by the Carnegie Institution for Science also warned that plants with fewer stromata would be less well capable of regulating microclimates, with possibly higher temperature extremes.

Nutritional value

There could also be ecological consequences to plant adaptation to higher CO levels. Australian research from 2008 suggests for instance koalas can’t properly digest eucalyptus leaves that formed under higher CO2 concentrations. The leaves would have lower nutritional value and contain more toxic tannins.

CO2 no limiting nutrient

The fact that plants actually decrease stromata with increasing CO2 on such short timescales indicates CO2 is not a growth-limiting nutrient to general plants, contradicting thoughts around a ‘CO2 fertilisation effect’, in which increases in CO2 levels would compensate themselves through increased biomass production – a view that was particularly prevalent in the US during the nineties, but is still heard in climate discussions from time to time.

© Rolf Schuttenhelm |

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