Linking Spectro-Functional Variability and Aquatic Plant Diversity

Due to their morpho-physiological peculiarities and wide phenotypic plasticity, aquatic plants - or macrophytes - occupy the extremes of the global spectrum of vegetation forms. Such heterogeneity results in contrasting patterns of diversity along ecological and geographical gradients. As a high-throughput technique, imaging spectroscopy is a feasible and efficient option for assessing plant functional diversity based on spectral proxies directly related to morphological and biochemical traits, which we define as spectro-functional traits. In this study, we used airborne hyperspectral data to assess inter- and intra-specific spectral diversity of floating and emergent macrophyte species in shallow freshwater systems in Italy, Hungary and Lithuania. Our results show that inter-site variability (including latitudinal and seasonal differences) modulates leaf structure and pigment balance. Furthermore, intraspecific variability accounts for a significant fraction of the total diversity in photophysiology and pigments (>20% of total diversity), and even more for density/biomass (LAI), about 50% of total diversity. Remotely sensed maps of spectro-functional macrophyte traits can capture fine-scale variability, between and within species, that would be difficult to detect from point measurements: a powerful addition to the technical toolbox in the hands of functional ecologists focusing on aquatic plants and biogeochemical processes they mediate.