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Carbon dioxide concentration reduces the width of the leaves
In the recently published "Proceedings of the National Academy of Sciences," British scientists pointed out that the primitive land plants of ancient times later evolved large leaves to absorb sunlight because the concentration of atmospheric carbon dioxide was continuously reduced to give them impetus. Compared with today's leaves, the leaves of plants 400 million years ago were much narrower and not so effective as "solar cells". Most of them were small sticks and they were called small leaves. Moreover, although the plants at that time had the ability to develop giant leaves in both gene structure and physiology, this process still lags 20 million years. This lag has plagued paleontologists for a long time. Recently, David Beerling and Colin Osborne of the University of Sheffield in the United Kingdom and William Chaloner of the University of London proposed a theory that the extremely high carbon dioxide level at that time prevented the evolution of leaves. They point out that compared with the present, the carbon dioxide level in the Devonian atmosphere is 10 times higher, and the stomata needed for the entry of CO2 into the leaves of plants are much less. These few pores also play the role of plant sweat glands, which cool the leaves by releasing water. The team’s computer model showed that, given the poor cooling ability of the leaves of the plants at that time, if the surface area of ​​the leaves and the solar radiation absorbed by them were to increase, the leaves could easily be destroyed by overheating. The researchers believe that carbon dioxide levels began to decline about 370 million years ago, and plants therefore need to increase the density of stomata in their leaves, so that large leaves also begin to have the ability to cool. In order to rigorously test their theories, scientists conducted extensive research on the records of leaf fossils, measured the leaf area of ​​approximately 300 plants, and also calculated the number of stomata in some leaves whose outer skin was not damaged. The results show that the rapidly falling atmospheric carbon dioxide level is in perfect agreement with the growing leaf area and stomatal density.