Intraspecific Variation in Leaf Trait Responses to Experimental Warming in Iris pumila Populations from Contrasting Habitats

Phenotypic responses to climate warming may differ among plant populations originating from contrasting habitats. To evaluate intraspecific variation in leaf trait responses to warming in Iris pumila, 40 genotypes from the Dune and Woods populations were exposed sequentially to ambient, +1 °C and +4 °C temperature regimes under controlled conditions. Functional leaf traits (specific leaf area, SLA, and leaf dry matter content, LDMC) and mechanistic leaf traits (specific leaf water content, SLWC; leaf thickness, LT, estimated from SLA and LDMC; stomatal density, SD; and the RGB-derived index I1, previously calibrated in I. pumila as inversely related to chlorophyll concentration) changed across the sequential temperature regimes. SLA, SLWC, LT and I1 increased, whereas LDMC and SD decreased. Dune and Woods genotypes differed in SLA, LDMC and I1, with higher SLA and I1 in Dune and higher LDMC in Woods. The phenotypic plasticity index (PIV) differed among leaf traits within each temperature contrast, with generally higher values for SD and I1 and lower values for SLA. Population differences in PIV were evident for LDMC and SLWC from ambient to +1 °C (Dune > Woods) and for LDMC from +1 to +4 °C (Woods > Dune). Trait-correlation structure varied across the temperature sequence, although evidence for overall correlation-matrix similarity was not robust to changes in trait composition. No statistically detectable differences in the magnitude of phenotypic integration were found among temperature regimes or between populations. Overall, leaf responses in I. pumila revealed trait-specific changes and population-dependent patterns across the sequential temperature regimes, reflecting the complexity of intraspecific responses to warming.