Scientists explain how leaf apex enhances water drainage

Chinese scientists have recently shown how the tiny apex structure in plant leaves controls water drainage and confers an evolutionary advantage.

The research was conducted by Prof. Jiang Lei's team at the Technical Institute of Physical Chemistry of the Chinese Academy of Sciences. Results were published online in PNAS Jan. 13.

The leaf is the basis of plant survival. Through evolution, leaves have developed means to help control the absorption of sunshine and rain. The apex, for example, is where water is shed from the leaf and thus affects how droplets are shed.

In rainforests—which are characterized by high precipitation and humidity—understory plant leaves must drain water fast to avoid water-induced rot and damage. The most famous evolutionary advance in rainforest leaves is the drip tip. Although biologists have known since the 1980s that the drip tip facilitates fast drainage, they didn't understand the role the apex played in this process.

According to Dr. Dong Zhichao, the study's corresponding author, the tapered shape of the apex causes reduced capillary resistance in droplets. At the same time, the steep orientation of the apex increases the effect of gravity. Together, the apex's shape and orientation increase instability, thus enhancing water drainage.

For Dong, understanding this mechanism not only increases our appreciation of the role tiny structures play in plant survival, but also provides inspiration for upgrading drainage facilities and anticorrosion architecture.

This is especially important since dripping modes characterized by high frequency, low retention and low volume help reduce soil erosion.

Ancient architects intuitively understood the efficiency of drip tips, since drip tiles in oriental palace roofs and gargoyles in cathedrals exhibit excellent drainage and anticorrosion ability.