Strengths and weaknesses of the use of functional traits in recent studies on macrophytes

Macrophytes are getting increasing attention because of their multiple roles in aquatic ecosystems. However, eutrophication and habitat degradation are threatening macrophytes globally. In this context, the use of functional traits (FTs), i.e. specific features measured at species/individual level, can give more quantitatively translatable information than the traditionally adopted taxonomic approach about their ecosystem functions. This research aims to elucidate the use of FTs in recent macrophyte studies and is preparatory to the macroDIVERSITY project (PRIN 2017), which uses spectral and phylogenetic diversity to map functional diversity in macrophyte communities. A systematic literature review focused on aquatic plants and functional traits was carried out on SCOPUS database (www.scopus.com). The latest 53 papers, published in 2019, were examined. The main topics emerging from these works on macrophyte FTs relate to: 1) the role of FTs in shaping communities; 2) macrophyte responses to environmental gradients; 3) application in monitoring anthropic pressure; and 4) how FTs mediate biotic interactions. We recorded that 27 studies involve only single or few species and therefore results are hardly exportable at the ecosystem level. The most used FTs include leaf economic and morphology traits. We noticed a lack of attention on root traits and an extended use of physiological traits that are difficult to measure in the field and on larger scales. We therefore advise to promote collection and processing of root traits, and to push forward the integration of remote sensing and classical approaches to clarify the role of macrophytes at multiple scales.