Thursday, September 28

Climate change prevents trees from carrying out photosynthesis

Fallen tree leaves. / File, Archive

Heat and lack of water put plants in ‘saving mode’ to avoid increasing energy consumption

Jose A. Gonzalez

Irritability, tiredness, boredom, stress, moodiness, lack of sleep. These are some of the consequences of high temperatures in humans, an impact that is also reflected in animals and plants. “Our data and analyzes suggest that a warmer climate will result in canopy leaf temperatures, likely leading to reduced carbon assimilation capacity and ultimately heat damage,” says Dr. Professor Chris Still of Oregon State University.

October, November and even December are synonymous with sidewalks covered by dry leaves, however, this fall, more and more, comes before September and also August. The heat and lack of water put the trees in ‘saving mode’ to avoid increasing energy consumption and survive high temperatures.

To survive, these plants need water and light to photosynthesize. In autumn, the hours of light decrease, so the leaves fall off the branches to avoid increasing consumption. In summer, the lack of water, increasing, causes the same action. “This does not mean that the tree is dying,” the experts point out. However, the situation is worrying: “Trees may be approaching critical thresholds of temperature stress faster than we expect,” says Still.

also suffer

Europe closed last meteorological summer (June-August) as the hottest summer period since 1880, according to data from the Copernicus Climate Change Service. Historical milestone also beaten in Spain with an anomaly of 2.2 degrees above the average, which means having exceeded the year 2003 by 0.4ºC, considered until now the warmest summer season since there are records, according to data from the State Meteorological Agency (Aemet).

“Trees may be approaching critical temperature stress thresholds faster than we expect”

Chris Still

professor at Oregon State University

A few atypical months with extreme temperatures in large parts of the country and that have ended with 42 of 90 days under the official name of “heat wave”. Plants have many ways to regulate temperature, either actively or passively, to maximize CO2 uptake and reduce water loss through the stomata (pores) in their leaves. “Photosynthesis is particularly sensitive to temperature,” the researchers Berry and Bjorkman note.

Leaf in autumn. /

File, Archive

Several studies indicate that as the temperature increases, the absorption of CO2 is greater. “Photosynthesis occurs more frequently at 21ºC”, several experts agree.

When temperatures get too high, plant leaves open pores on their surface, called stomata, to cool down. In addition, these also allow plants to absorb carbon dioxide from the atmosphere, but when fully open the leaf can lose too much moisture. A tree can release up to 604 liters of water per day through the stomata (small pores) in its leaves, a figure that drops to 190 liters in summer. “If plants cannot maintain temperatures below critical thresholds where damage occurs, then physiological acclimatization becomes critical for plants to continue to photosynthesize,” the researchers reveal.

thermal exhaustion

In their research, Still and the other researchers at Oregon State University focused their eyes on trees in North and Central America. “Over much of the hot, humid tropics, leaf temperatures are already approaching or exceeding thresholds for positive net photosynthesis,” they write. “Trees may be approaching critical temperature stress thresholds faster than we expect,” Andrew Richardson, a professor at Northern Arizona University and co-author of the study.

A tree can release up to 604 liters of water per day through the stomata of its leaves, a figure that drops to 190 liters in summer

The study shows that canopy leaves heat up faster than the air, are warmer for most of the day, and only cool below air temperature in mid-afternoon or late afternoon. “Future climate warming is likely to lead to even higher canopy leaf temperatures, which would negatively affect forest carbon cycling and increase the risk of forest mortality,” they warn. “If canopy photosynthesis declines with increasing temperature, it will reduce the ability of forests to act as carbon sinks,” adds Still.

However, thermal is not the only stress that plants face, since water is another of the great concerns of experts. Without water, plants are unable to capture CO2 from the atmosphere. The absorption of carbon dioxide is linked to the loss of water through a diffusion process. When the CO2 reaches the interior of the leaves, the water vapor escapes into the atmosphere. A balance, usually negative, because for each molecule of CO2 absorbed, about 400 molecules of water are lost.

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