Woody clockworks - trees have a built-in alarm clock

Last updated: 30 Aug, 2013

For photosynthesis to work, small pores in the leaf called stomata are open during the day. Atmospheric CO2 moves through the stomata into leaves, where the photosynthetic apparatus converts it into carbohydrates. While necessary for absorbing carbon, open stomata unavoidably lose water. This is, on the one hand, a positive effect, since evaporating water cools the leaves and the water stream is essential to transport nutrients to the top of the tree. On the other hand, this atmospheric water loss can, under dry conditions, be harmful for the plant, leading to wilting and ultimately to death. At night, when photosynthesis is not active and no CO2 uptake is possible, trees close their stomata largely to avoid unnecessary water loss. However, this nocturnal stomatal closure is not complete.


Photo from Woody clockworks: circadian regulation of night-time water use in Eucalyptus globulus

A controlled-environment whole-tree chamber.


Indeed, in a new study, published in New Phytologist, an international research team led by Dr Víctor Resco de Dios, from the Hawkesbury Institute for the Environment at the University of Western Sydney, has observed that the dynamics of opening and closing the stomata during the night, and therefore whole tree water loss in the dark, is regulated by internal plant control. After sunset, stomatal closure reaches a maximum, but briefly after midnight the stomata open again and facilitate transport of water from the soil to the atmosphere through the plant. It has long been known that many cellular processes in plants, just like in animals, have an internal timer that operates on a molecular level with a cycle of approximately 24 hours (circadian). In their work, the team of Dr Resco de Dios has shown for the first time that this molecular clock can affect the water balance of an entire tree. Arthur Gessler, co-author of the study from the Leibniz Centre for Agricultural Landscape Research explains: “The trees, with help from their internal alarm clock, can calculate the time of sunrise in advance, which allows the plant to conduct photosynthesis when the first sun rays reach the plant.”


The fact that not only external factors, but also the internal clock, controls the opening of stomata, and thus water use by trees and forests, has far-reaching implications when modeling the water balance of ecosystems and thus their impact on climate. Particularly when long-term trends in environmental conditions are changing, current models that do not consider this internal regulation may not be suitable to accurately predict water requirements and water use in forest ecosystems.


Resco de Dios V, Díaz-Sierra R, Goulden ML, Barton CVM, Boer MM, Gessler A, Ferrio JP, Pfautsch S, Tissue DT. 2013. Woody clockworks: circadian regulation of night-time water use in Eucalyptus globulus. New Phytologist, in press.