Plasticity to daylength of Iris pumila leaf phenological traits
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Plastic responses to photoperiod of Iris pumila leaf phenological traits were investigated in two populations experiencing contrasting light conditions in the dune system at Deliblato Sands (44degrees48' N, 38degrees58' E; Serbia, Yugoslavia). The population "Dune" occupied an exposed area at the top and slope of a relatively large dune, and the population "Woods" was situated in the understory of a Pinus nigra stand. Plants developed from rhizome segments of 15 and 12 clonal genotypes sampled individually in an exposed and a shaded site, respectively, were grown:under alternating daylength conditions (long day, 16h; short day, 8h) in an environmentally controlled growth room, and scored for a number of leaf traits (live and senescent leaf number per ramet, leaf longevity, and phyllochron). The photoperiodic treatments used significantly affected the phenotypic values of all traits analyzed, regardless of the population origin. Leaf longevity decreased, whereas the proportion of senescent to live leaves increased under short as compared to long photoperiod. The amount of plasticity to daylength appeared to be strongly trait specific: senescent leaf number was the most plastic, and live leaf number per ramet the least plastic trait, in both populations. The factorial ANOVAs did not reveal a significant population effect on any of the leaf traits observed, except the phyllochron, indicating the presence of genetic variation between populations only for that particular trait. A statistically significant interaction term obtained in each of the ANOVAs provides the evidence of the, existence of genetic variation for plasticity in all the leaf phenological traits studied. Genetic correlations among all trait pairs were close to zero and mostly statistically nonsignificant, indicating that the analyzed L pumila leaf phenological traits are not genetically constrained to evolve by natural selection toward their optimal reaction norms within each light habitat.