How to measure flower UV-reflectance using digital photography

Flower ultraviolet (UV) reflectance strongly influences insect ability to detect flowers and locate pollen-nectar sources. Although included in the TRY database, the lack of a cost-effective standardized method of measurement hampers the availability of information on this key floral trait. Digital photography and image processing allow for a novel approach to flower UV-reflectance measurement that is both accessible and accurate. We used a UV-LED light and a mirrorless camera with a filter, which represents a low-cost equipment for narrow emission/reflection photography (350-380nm). Flowers were photographed with two standards of known reflection, and UV-reflectance values were obtained through an open-source image processing software. We measured UV-reflectance for 57 plant species typical of European semi-natural grasslands. Our values substantially matched the categorical classes obtained through analog photography available in TRY and showed a highly significant relationship with spectrophotometric measures. The method here proposed overcomes the one based on analog photography and subjective visual estimates, and represents an easy and low-cost alternative to spectrophotometry. It may promote the standardized measurement of flower UV-reflectance and broaden the information of this trait globally, meeting the needs of functional ecology and trait-based community assembly studies.