Over time, researchers have been wondering why leaves reached giant sizes in hotter areas of the globe, and why they decreased in size as latitude increased. After many years of research, they might have finally found an answer, and tied different climate factors to these varying patterns of leaf size among the globe.
Temperature is the biggest factor which determines leaf size
To find the answer, a team of researchers from Macquarie University in New South Wales went in 682 regions in the world, and studied the size of 7,670 leaves. They found the main factor which influenced how leaf size was the difference in temperature between night and day. In addition, moisture and irradiance are also important.
Therefore, plant species with big leaves are more often found in areas with a hot and humid climate. Smaller leaves are related to arid conditions, and can appear in both hot and cold regions. Also, as latitude and altitude increases, the leaves get smaller.
Leaf size pattern might differ
The conditions in hotter areas of the globe are perfect to maintain a big leaf size. Researchers explained how, during the day, leaves accumulate a so-called ‘leaf energy budget’. Since big leaves are thicker, their exchange of heat with the air is slower, so there is a big temperature difference between them. To cool themselves, they have to ‘sweat’ and lose water. Therefore, the high temperatures cause these leaves to need more water to survive, and this exact need made them evolve as bigger and thicker.
Of course, these patterns can differ. As climate change causes average temperatures to increase, the average leaf size also increases. Also, a different accumulation of energy during nighttime can cause leaves in cold areas at high altitude to increase. However, there is a global pattern which can be applied everywhere, and researchers have analyzed it in a study published in the journal Science.
Image Source: Max Pixel