Increased atmospheric carbon dioxide makes trees use water more efficiently

May 11, 2015, University of Exeter
Tops of broadleaf trees. Credit: I. Heinrich, GFZ

The increase in atmospheric CO2 concentration has allowed trees across Europe to use their available water resources more efficiently, new research has shown.

Over the course of the 20th century, the so-called water use efficiency has risen nearly 20% from the increase in atmospheric CO2 concentrations.

These results, produced by an international research team, including experts from the University of Exeter, are reported in leading scientific journal Nature Climate Change.

Trees take up carbon dioxide from the air through tiny pores on their leaves called stomata and they lose water through these same pores.

When the CO2 concentration in the air increases, the size of the stomatal opening reduces to regulate the amount of carbon acquired which minimises the water lost. As a result the so-called water use efficiency increases.

In this study the researchers used measurements of carbon from tree-rings and computer models to quantify tree and forest responses to both climate variation and increased atmospheric CO2 concentrations.

"Tree-ring data provide one of the unique opportunities to obtain long-term records of ecosystem responses to climate change", said David Frank, a Dendroclimatologist at the Swiss Federal Research Institute WSL and collaborator at the Oeschger Centre for Climate Change Research, University of Bern.

The researchers used data from 23 tree ring sites spanning Morocco to Norway to quantify variation in water use efficiency - the amount of water required to produce a given amount of carbon - and a basic measure of plant and ecosystem economy.

Typical annual ring pattern of Juniperus excelsa, with widely varying and sometimes very narrow growth ring. Credit: I. Heinrich, GFZ

Professor Pierre Friedlingstein, Chair of Mathematical Modelling of Climate Systems at the University of Exeter and one of the authors of the report, said: "The observed water use efficiency increase, in response to atmospheric CO2 increase, is something we are able to reproduce with global vegetation models giving us more confidence in the whole ecosystem response to CO2.

"However, our models simulation also indicate that globally, other drivers, such as climate change and land use change, also impact on the plant hydrological cycle."

"By measuring the ratios of heavy to light carbon isotopes of tree-ring cellulose we are able to reconstruct various physiological metrics such as water use efficiency and their environmental drivers", said Kerstin Treydte co-author of this study and a specialist in tree-ring isotopes at the WSL.

On average, 100 kilograms of water released by a tree through the stomata equates to one kilogram of tree biomass created. The study showed that reduced stomatal opening increased water use efficiency by 14% in broadleaf species and by 22% in needleleaf species.

Despite the CO2 induced stomatal closure, the models showed that the consequences of a warming climate - lengthened growing seasons, increased leaf area and increased evaporation - resulted in a 5% increase in forest transpiration - the cycle of water through trees. This increase cancels out any savings in water from improved efficiency. Plants are therefore unlikely to reduce levels of atmospheric water vapour - an important greenhouse gas. It is also unlikely that plant responses to increased CO2 will substantially increase soil moisture or river run-off.

Explore further: Increase in CO2 has not stimulated growth of tropical trees

More information: Water-use effciency and transpiration across European forests during the Anthropocene DOI: 10.1038/NCLIMATE2614

Related Stories

Increase in CO2 has not stimulated growth of tropical trees

December 16, 2014

Since the start of the industrial revolution in 1850, atmospheric CO2 levels have increased by about 40%. However, contrary to expectations, the growth of tropical trees has not increased as a result. The prediction that ...

Araucarias gauge ancient levels of carbon dioxide

April 29, 2011

One way of telling how much carbon dioxide was in the atmosphere in the past is by counting pores (or stomata) in leaves – the tiny openings plants use to absorb CO2 and lose water. It may seem far-fetched, but plants ...

Ocean carbon uptake more variable than thought

November 13, 2014

The Earth's oceans are thought to have taken up about one quarter of the carbon dioxide (CO2) that humans pumped into the atmosphere in the past 2 decades. While this drives acidification and has consequences for sea life, ...

Loss of eastern hemlock will affect forest water use

May 9, 2013

The loss of eastern hemlock from forests in the Southern Appalachian region of the United States could permanently change the area's hydrologic cycle, reports a new study by U.S. Forest Service scientists at the Coweeta Hydrologic ...

Ancient forests stabilized Earth's CO2 and climate

January 23, 2014

UK researchers have identified a biological mechanism that could explain how the Earth's atmospheric carbon dioxide and climate were stabilised over the past 24 million years. When CO2 levels became too low for plants to ...

Recommended for you

New evidence for plume beneath Yellowstone National Park

March 20, 2018

A pair of researchers from the University of Texas has found what they claim is evidence of a plume beneath Yellowstone National Park. In their paper published in the journal Nature Geoscience, Stephen Grand and Peter Nelson ...

Thawing permafrost produces more methane than expected

March 20, 2018

Methane (CH4) is a potent greenhouse gas that is roughly 30 times more harmful to the climate than carbon dioxide (CO2). Both gases are produced in thawing permafrost as dead animal and plant remains are decomposed. However, ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.