Trees control leaf temperature, but how much?

2008/06/12 Roa Zubia, Guillermo - Elhuyar Zientzia

• Botanika

An article published in the journal Nature has generated controversy. In this article, a team at the University of Pennsylvania has proposed that trees are able to accurately control leaf temperature. According to them, the fact that it is winter or summer and is north or south, gets that the temperature of the leaves does not go away from 21ºC. The temperature of the leaves remains almost

constant can be important for the tree from the point of view of photosynthesis, since it is a very sensitive process to temperature. 21°C is the right temperature for photosynthesis. If it cools slightly, even though they are few degrees, the proteins involved in photosynthesis are buffered and the chemical reaction they cause slows down; if heated slightly, the membrane of the leaf cells is distorted and retains the proteins of photosynthesis. Thus, by controlling the temperature of the leaves, the tree achieves perfect conditions for photosynthesis. The

chemistry of trees is not like the largest animal, they cannot control temperature by chemical reactions. But they use other systems. They can change the angle of the leaves so that they receive more or less heat from the Sun. In addition, fir trees and many northern trees accumulate their leaves together to form layers of air that protect them from the cold. Moreover, leaf stomata can also

control open and closed leaf temperature. According to measurements from the Pennsylvania team, control is very accurate. Other researchers have criticized the measurement system. The

Pensylvania team has studied the oxygen atoms of the tree trunk, namely

the ratio between two oxygen isotopes (16 oxygen and 18 oxygen). In air, this ratio varies with temperature and humidity. Therefore, with the data of a given moment and place, it can be compared with the proportion of isotopes accumulated by the tree in the trunk. If there are differences it is considered that it is due to the natural temperature of the leaves, from where the temperature can be calculated at that time. Thus the Pennsylvania group has measured the

temperature of the leaves, but the results of these measurements do not coincide with those made long ago and with more correct methods. For example, the placement of thermocouples in the leaves has allowed some researchers to measure very variable temperatures in the leaves. Also the German corner, researcher who measured the influence of the air layers between the leaves, has criticized the method of measurement, since the trees do not grow at all times and therefore do not accumulate oxygen in the trunk.

Photo: Morguefile