From My scrapbook :: 5

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Size of leaves

Trees sleeping at night

I am back on the theme of trees. They somehow fascinate me and I can just not get enough of them.

Global warming has now become the driver of numerous researches about its effects on the planet’s flora and fauna. While some researchers have found significant relationship with global warming of shrinking skulls of moose that are residents of Michigan’s Isle Royale others are out investigating the effects changes in temperature have on the size of the leaves of various plants.

It has been said that plants have a delicate balance to strike when it comes to the size of their leaves. The leaves have to be large enough to absorb sunlight for photosynthesis but not so big as to use up a lot of water to cool them. New researches have shown that leaf size in most plants is actually determined by the difference between temperature of the leaf and the air temperature around it and the changes that occur between hot days and frosty nights. These results were obtained after analyzing more than seven thousand kinds of plants across the world.

Earlier the understanding in respect of the size of the leaves was more straightforward. It was held that those that were closer to Equator had larger leaves and as one moved towards the Poles the sizes of leaves progressively became smaller. Tropical rain

forests were full of plants with large and lush leaves while in arid areas and towards the Poles plants get by with tinier and tinier foliage. Researchers have, however, shown that in most plants limits to the size of the leaves are more set by the risk of freezing at night than by the risk of overheating during the day. The researchers also add that water has also a role to play. If there is enough water in the soil there would perhaps be no limit to the size of leaves.

 As climate change affects both temperature and water availability, understanding how and why plants will respond to such changes will be critical. The researchers have claimed “their model can help predict which plants, thanks to leaf size, will thrive in the new world” with progressively changing climatic patterns.

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Sleeping trees

That plants go off to sleep at night has all along been known. In our childhood we were told by mother never to tear off a leaf or pluck a flower at night as the plants go off to sleep as soon as darkness sets in. This advice was purely anecdotally sourced. Now researchers have proved that what we were told in our childhood is, in fact, true. Obviously, whatever was handed down to us had some kind of wisdom behind them.

Using laser scanners researchers from Austria, Finland and Hungary have attempted to measure “sleep movements” of fully grown trees. By monitoring a series of laser points on the trees they discovered that the trees more than 16 feet high dropped their branches by not around 4 inches at night. The experiment was carried out in two different countries, Finland and Austria in calm conditions with no winds.

 The scanners used infra red light for a fraction of a second on individual points on a tree. Infra red light is reflected by leaves and hence these were used to record their nocturnal movements. A terrestrial scanner was used to precisely map out a set of points on two silver birch trees – one in Austria and the other in Finland.  By making a series of these maps between dusk and dawn and measuring the displacement of each point they were able to trace how the trees moved during the course of the night. The leaves and branches of the trees were shown to droop gradually; the lowest they did so was until around a couple of hours before sunrise. However, with a few daylight hours they would be wide awake, as it were, assuming their daytime stance, as erect as they could be.

 It is being speculated that drooping may be caused by internal pressure in the plant cells which, it is felt, is because of photosynthesis. At night photosynthesis drops and hence production of sugars in the cells also drops, reducing the pressure. At the same time some researchers feel that by drooping their branches and the leaves on them the trees might be allowing their branches to ‘rest’ after using cell pressure during the day to angle their leaves to catch sunlight. Some others feel that the drooping of the branches and leaves could be a way to conserve energy.

Quite clearly, more researches are called for. Hopefully, these investigations will reveal the nocturnal secrets of trees which, presently, are unknown to most of us

*Photo from internet