A large sheet is not convenient to plants for two reasons – it is possible to quickly dry up in the summer and it’s easy to freeze in winter.
The size of leaves from different plant species may differ in a thousand times, for example, the Australian eutaxia Eutaxia microphylla or Ling area of the sheet is on average 1 mm2, and the Abaca, or textile banana – 1 m2.
Obviously, this difference arises from the fact that different plants grow in different conditions, and it is easy to see that the smallest leaves from those deserts and semi-deserts, and the biggest – tropical species. But what factors more affect the leaf size?
We know that the leaf of a plant literally absorbs carbon dioxide, which in the process of photosynthesis glucose is obtained. Carbon dioxide enters the leaf through special openings on its surface called stomata. Through these same holes, the sheet emits water. The evaporation of water leaf is called transpiration, and transpiration is maintained due the movement of fluid through the vascular system of the plant from the roots to the top. But in hot weather from the sheet crashes too much water, so that it can wilt and dry up. It would be possible to close the stomata, but how to needed for photosynthesis carbon dioxide?
We already wrote about how plants solve the problem of humidity and temperature using different types of photosynthesis. Another solution anatomical: try to optimize the leaf size. More than a hundred years ago ecologists came to the conclusion that tropical plants have got big leaves just because of where they grow, often and abundant rains, the famous tropical storms. Indeed, if conditions allow, why not increase the sheet as possible?
In the 60-70-ies of the last century on the issue tried to look otherwise, taking into account that many of the plants that live in hot and dry geographic areas typically vulnerable to overheating, especially in summer. Escaping from overheating, the plant increases transpiration (can you say, heavily “sweating”), but if you have large leaves, there is a danger of losing too much water for cooling. The solution is to reduce the area of the leaf. This explanation is suitable for desert plants; in addition, it becomes clearer why large leaves of those growing up in the shade and coolness, for example, in the undergrowth, under the canopy of crowns of higher trees.
However, many could be noted that this explanation places much limping. For example, the tropics have not only humid but also hot – it turns out that in some cases, the heat can survive and with large leaves. In addition, overheating, especially in summer days, threatened plants in many other regions, is generally much cooler than the desert and semi-desert. Meanwhile, the leaves of plants in cooler regions is much larger than that of desert species.
Researchers from the Australian Macquarie University, together with colleagues from the UK, Estonia, China, Spain, USA, Argentina and Canada have found new regularities linking the sheet size with the environmental conditions in which the plant lives.
The authors were compared over 7600 species of plants from all continents and all climatic zones. In an article in Science, they write that the size of the sheet determine several factors: the daytime temperature, night temperature, amount of rainfall and the amount of solar radiation that reaches the plants (the amount of radiation depends on the distance from the equator and average cloudiness).
The result is that where it was Sunny, hot and dry to grow plants with small leaves, because in such plants the main thing – not to overheat and not lose a lot of water. Where it was Sunny, hot and humid, the leaves will be large: here the plants can spend as much as necessary water for cooling.
But where it is very cold, the leaves will again be small. It turned out that in cold regions the main constraint is not the daytime temperature in the hottest month and the night temperature of the coldest – in other words, plants are no longer afraid to overheat and freeze.
The fact that each sheet keeps the surface layer of stationary air which serves as a heat insulator. The large leaves of this layer is thicker, therefore, on the one hand, it’s harder to give off heat, on the other hand, cooled down, they are harder to keep warm. And if the night gets especially cold and long, it is the night temperature becomes the main factor determining the largest size of the sheet.
However, in the same tropics, not all plants are able to grow huge leaves. However, it is worth to remember that day and night temperatures, coupled with rain, so to speak, limit the range of possibilities. It should be understood that in the humid tropics plants may not pay attention to the heat, because here they are not threatened to dry up.
And then it may work for other structural and physiological factors when a tree or Bush will “decide” that it is more profitable to have many small leaves or let the leaves be few, but they are great.
Themselves the authors acknowledge that their analysis did not take into account the influence of soil, but the influence of climate and soil can also affect the size of the sheet. But, whatever it was, already the results obtained, can be useful in a purely scientific and in a practical sense. For example, the size of leaves of extinct plants can more accurately determine what the climate was dominated on the Ground in a particular era.
If we want to replant some kind of new territory, comparing its leaves with the climate at its new location, it is possible to understand in advance how well would this kind of feel and, if we are talking about a crop, whether it will be there quite productive.
© 2017 – 2019, paradox. All rights reserved.
