When Genetic Diversity Is Low: The Effects of Ploidy Level on Plant Functional Trait Expression in <i>Spartina</i> Under Global Change

Whole genome duplication (WGD or polyploidization) events shape plant evolution, altering ecological responses and plant traits, particularly those related to cell and tissue size. We studied genetic diversity and phenotypic plasticity in <i>Spartina</i> populations, focusing on hybrid (<i>Spartina × townsendii</i>) and allopolyploid (<i>S. anglica</i>) cytotypes in Wadden Sea salt marshes. Our results reveal low genetic diversity in both cytotypes and a complex response of plant traits to global change factors (drought, elevated CO₂ concentration). While WGD increased stomatal length, plasticity varied between cytotypes, with allopolyploids showing higher plasticity, especially under elevated CO₂. Biomass allocation patterns differed between cytotypes under global change conditions, suggesting distinct effects on ecosystem functioning, such as belowground carbon sequestration and cycling. The allopolyploid's comparatively fewer, larger-diameter stems may affect aboveground ecosystem functions differently, including sediment trapping and the slowing of tidal currents. Despite similar genetic backgrounds, allopolyploids did not consistently exhibit higher plasticity, challenging previous assumptions. Our findings highlight the complex interplay between hybridization, WGD, phenotypic plasticity, and ecosystem responses to global change, emphasizing the importance of considering polyploidization in understanding plant adaptation and evolutionary dynamics.