Bracts and basal leaves in Hacquetia epipactis differ in their spectral signatures

Abstract

Hacquetia epipactis is an understorey species that develops leaves, flowers, and fruits before the canopy layer closes. Its umbels are supported by green bracts. We examined the functional traits of these bracts and basal leaves for specimens, sampled at two altitudes. In this view, their specific leaf/bract area, biochemical, and optical properties were analysed over the course of their development in order to detect differences and changes in both structures. For lowland specimens, specific bract area decreased with age. An increase in UV-absorbing compounds over time was found for both locations. These were negatively related to reflectance in the UV range for basal leaves, whereas for bracts UV reflectance increased with age. We observed an increase in photosynthetic pigment contents during the development of bracts/basal leaves, which resulted in increased absorbance of photosynthetically active radiation for specimens from both altitudes. Detrended correspondence analysis plot based on the reflectance of bracts/basal leaves showed clustering of samples from different age classes with no respect to location. Redundancy analysis revealed high importance of bract/basal leaf biochemistry in explaining reflectance. UV-B- and UV-A-absorbing compounds explained 13% and 8% each, carotenoids 9%, while anthocyanins and chlorophylls explained additional 4% of the reflectance spectra variability. Bracts and basal leaves displayed similar contents of photosynthetic pigments, which indicates their important photosynthetic function for both structures. The development of bracts/basal leaves showed greater influence on the examined parameters in comparison to altitude.