An article by a researcher from the Estonian University of Life Sciences was published as the cover story for Science magazine

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Global comparison of leaves from the same species of plant may prove to be quite different. Take, for example, the houseplant Monstera deliciosa, the leaves of which are rather small in the climate of Estonia in comparison with members of conspecifics growing in the tropics.

An international group of researchers, including Ülo Niinemets from the Estonian University of Life Sciences, has provided a new explanation in Science magazine regarding the diversity of leaf size.

While the leaf of a Ling Heather may cover less than a square millimetre, the leaf of a banana plant may cover an entire square metre. The difference is more than one million times.

There may be a difference of up to 100,000 times in the leaves of the same species of plant in different locations around the world.

As early as the 19th century, phytogeographers noticed that the leaves of plants growing in the tropics were bigger; however, a precise description has yet to be given on how the latitude and climate conditions of the earth are connected to plant leaf size.

It was observed long ago that large leaves are characteristic of humid tropical areas, while leaves in deserts and arctic areas tend to be rather tiny in comparison. Attempts have been made to explain these differences through variations in temperature and humidity conditions.

And now, 17 researchers from across the world, including Estonia, have undertaken a major research project and analysed the links between the leaf size of more than 7000 of the world’s plant species and the climate conditions of their respective habitats.

Researchers modelled plant leaf energy input and output during the day and at night in comparison with the leaf’s atmosphere.

It turns out that the daily maximum temperature and minimum evening temperature are both critical when it comes to the development of leaf size. If the leaf is too big, night frost or simply evening coolness may easily damage the leaf.

So far this factor has only been fully appreciated in the case of high elevation plants, but researcher Ian Wright from Macquarie University in Sydney, Australia, along with his colleagues, including Ülo Niinemets, from the Estonian University of Life Sciences, have now discovered that the threat of evening frost has a much greater global impact on leaf size.

This knowledge provides the opportunity to create a new generation of vegetation models. Namely, the effects of leaf temperature and the water regime are of key importance in photosynthesis, which in turn is very important knowledge for cultivating plants within the context of climate change.

The translation of this article from Estonian Public Broadcasting science news portal Novaator was funded by the European Regional Development Fund through Estonian Research Council.