Epiphyton alters the quantity and quality of radiation captured by leaves in submerged macrophytes

• The presence of the epiphyton affected leaf optical properties of macrophyte species.
• Removal of the epiphyton resulted in a significant increase in the leaf reflectance.
• Removal of the epiphyton resulted in a significant increase in the leaf transmittance.
• Epiphyton alters especially absorption of the short-wavelength radiation.

This study investigates the effects of the epiphyton and the leaf morphological and biochemical properties on the quality and quantity of radiation reflected from the adaxial leaf surface and radiation transmitted through the leaf tissue. The radiation in the range from 290 nm to 800 nm was analysed for submerged leaves of Potamogeton perfoliatus, Potamogeton lucens and Sagittaria sagittifolia. In all of these plant species, the epiphytic algal community was dominated by the diatom Cocconeis placentula. The presence of the epiphyton had more pronounced effect on the amount of transmitted light compared to the amount of reflected light. Most of the variability of the reflectance spectra was explained by the epiphyton dry mass at the adaxial surface (15%). Redundancy analysis to explain the variability of the transmittance spectra showed that the epiphyton layer at the abaxial surface of the leaves has a more important role than that at the adaxial surface, with 18% and 3% of the spectra variability explained, respectively. An additional 21% of the transmittance spectra variability was explained by the leaf carotenoid content. Removal of the epiphyton from the adaxial leaf surface resulted in a significant increase in the leaf reflectance along the spectra, with pronounced differences in the UV, violet and blue ranges. The transmittance spectra measured after removal of the epiphyton also showed a marked increase in the UV, violet and blue ranges. This demonstrates the important role of the epiphyton dominated by diatoms for the prevention of potential harmful effects of short-wave radiation.