Using an artificial model of a leaf, scientists have unveiled a mathematical principle underlying how leaf veins are arranged to enable water to perspire as fast as possible.
Because water perspiration is closely linked to how plants absorb CO2, the findings could help researchers learn about past climates by studying the patterns of veins found on fossilized leaves.
Water evaporation helps leaves stay cool and provides the pull that lets plants lift nutrients from the soil. But during photosynthesis, when plants open up the pores on the underside of leaves to absorb CO2, water escapes from those pores at an accelerated pace. “The same membranes that let CO2 inside also let water outside,” says Maciej Zwieniecki of HarvardUniversity’s Arnold Arboretum. Leaves then need abundant water flow to avoid dehydration. And the more CO2 a plant absorbs, the more energy it can take in from the sun through photosynthesis, and the more it can grow. Evolution should thus favor a distribution of veins that can carry water through the leaves at a fast pace.
Zwieniecki and his collaborators write in the July 8 Proceedings of the National Academy of Sciences that, on average, the distance separating the veins that pump water through leaves is about the same as the distance separating the veins from the leaves’ surface.