Being Female Matters: Drivers of Spatial Genetic Structure in Clonal White Poplar

In plants, Spatial Genetic Structure (SGS) is shaped by gene dispersal and effective population density and is further modulated by life-history traits such as clonality and dioecy. However, the combined effects of these factors on SGS remain unclear, particularly in tree species. Here, we examined how clonal reproduction shapes SGS and whether dioecy compounds this pattern in Populus alba (white poplar), a key component of riparian forests. Using 15 nuclear microsatellite markers and population genetic analyses of 1,068 individuals, we investigated sex-specific patterns in semi-natural and urban stands. In the studied stands, clonal growth predominated, with compact clonal architecture and occasional long-distance spread. Our results indicate that clonality intensifies SGS, with a nearly twofold stronger effect at the ramet level than at the genet level. Our results support the assumption that differences in clonal architecture between female and male individuals can generate sex-specific spatial patterns and thereby influence population genetic structure, with stronger SGS in female ramets (Sp = 0.129 and 0.177 in the semi-natural and urban stands, respectively) than in male ramets (Sp = 0.115 and 0.066). A comparison of semi-natural and urban stands indicates that the intensity of spatial genetic structure reflects the combined effects of clonal structure and habitat-specific factors. Spatio-temporal variation in resource availability and disturbance regimes may contribute to these patterns by influencing population dynamics. Given the degradation of Europe's riparian forests and the limited knowledge of genetic resources of white poplar, understanding these spatial processes is crucial for informing restoration efforts and the sustainable management of genetic resources of the species. Our study revealed that the observed SGS patterns are strongly habitat-dependent; therefore, the protection and restoration of dynamic riparian forests should adopt an integrated genetic-environmental approach to ensure their long-term adaptive potential under ongoing climate change.