How wet are water plants? Determination of macrophyte leaf water repellency

Leaf water repellency (LWR) is a very important plant trait that influences plant performance in many different ways in different habitats. Being always in contact with water, the conditions for aquatic plants (macrophytes) are very different than for terrestrial plants and many of the advantages of high water repellency are less relevant for submerged macrophyte leaves. This paper is the first to determine the LWR of submerged leaves of 6 common macrophyte species by measurements of a contact angle between a water droplet and the leaf surface. Contact angles varied between 30° and 80°, classifying all species as hydrophilic. Yet significant interspecific differences were found. Differences between the ab- and adaxial leaf sides were small. The presence of a biofilm changed contact angles across species by about 20° in a positive or negative direction, depending on periphyton mass. Potential ecological effects of variation in LWR are discussed for macrophytes and manipulation of the biofilm by the plants to optimize LWR is hypothesized.