Analysis of genetic diversity and phenotypic plasticity in Phragmites australis and Nuphar lutea. A case study from Northern and Central Italy

Wetlands are highly productive environments with an increasingly recognized economic, social, and ecological value. The high primary productivity characterizing wetlands is mainly due to a dense macrophytes vegetation, which plays several roles in biological processes and associated ecosystem services. Like terrestrial plants, the persistence and resilience of macrophytes is affected by altering environmental factors such as temperature, salinity, the availability of nutrients and light and by the intraspecific diversity dimension. The intraspecific diversity leads the species' adaptive response to biotic and abiotic environmental factors and plays a crucial role in populations' ecological and evolutionary dynamics. Therefore, understanding patterns and processes of genetic and phenotypic intraspecific diversity become essential for environmental, evolutionary and conservation studies. Moreover, it is crucial to determine the role of selective and neutral processes in driving observed differentiation. In the last years, several studies have investigated the potential of natural selection on morphological evolution by comparing phenotypic divergence with neutral genetic divergence via a PST/FST approach. In this context, we aimed to assess and compare the genetic differentiation and functional traits variation at the intraspecific level of two macrophyte species, the helophyte Phragmites australis and the emergent hydrophyte Nuphar lutea. We first analyzed the AFLP-fingerprinting profiles and morphological and biochemical traits in both species sampled across several lakes in north-central Italy. The functional traits were estimated using both proximal measures on the leaves (Leaf Area, Leaf SLA, Chl-a and Chl-a/Chl-b) and inversion of the PROSPECT model (Chl_ab, LMA, LDMC, and Nmesophyll). Then, we investigated the correspondence between the degree of population differentiation in neutral genetic markers and the quantitative traits, as measured by FST and PST indices, respectively. As for P. australis, results showed that traits variability was almost entirely shaped by phenotypic plasticity, except for three traits: Leaf SLA for Chiusi, Chl-a for Iseo and the Chl-a/Chl-b ratio for the Pusiano-Annone site. As for N. lutea, results were much more complex and heterogeneous. The phenotypic plasticity and genetic diversity appear to have affected the variability of different traits within each site, except for Pusiano-Annone where traits variability was mostly due to genetic diversity (Tab. 1). This work allowed to understand the contribution of genetic variability and phenotypic plasticity to the traits' variability of P. australis and N. lutea and to propose new considerations on health conditions or response to environmental factors of both species.