Abstract: Traditional studies of plant elemental composition have mainly focused on the concentrations of C, N and P and stoichiometric ratios among different plant species. Little attention was paid to the intraspecific variation of the elementome and the underlying mechanisms including phenotypic plasticity and adaptive evolution. We conducted salinity manipulation experiments in two common gardens with two lineages of a widespread grass (Phragmites australis), measuring ten element concentrations of the leaves and roots. The genetic distances and epigenetic distances were calculated from SSR and MS-AFLP markers, respectively. In a principal component analysis, the root elemental contents contributed to the first two principal components (PC1 and PC2), and the leaf elemental contents contributed to PC3 and PC4. The PC1 was affected by salinity, while the PC2 was affected by salinity, climate and their interaction. The PC3 was affected by salinity, while the PC4 was affected by lineage. Mantel tests showed a significant correlation between epigenetic and environmental distances as well as between epigenetic and genetic distances. The contribution of genetics to epigenetic variation was larger than the environment. Genetic and epigenetic variation was associated with different PCs. The elementome is decoupled between leaf and root, and the root elementome had a larger variability. The leaf epigenetic variation depends on the genetic variation, and is also induced by the external environmental changes. Intraspecific elementome variation reflects environment more than genetic and epigenetic variation. These insights shed light on the underlying ecological mechanisms that drive the intraspecific variation of the elementome.

Key words: plant biochemical traits, plant stoichiometry, adaptive evolution, wetland plant, common reed