Stomatal density in Quercus petraea and Q. robur natural populations in Northern Turkey

This study examined variation of stomatal density in two populations of Quercus petraea (Matt.) Liebl. and two populations of Q. robur L. from northwestern Turkey. Stomatal density was determined in fully expanded and dried leaf samples that were collected from trees under natural conditions. Stomatal densities of Q. petraea and Q. robur varied from 186 to 459 per mm2 (mean value: 333 stomata per mm2) and from 397 to 826 per mm2 (mean value: 517 stomata per mm2), respectively. Significant differences in stomatal density were found between these two oak species in Turkey as well as between populations within species. Strong and significant negative correlations were observed between stomatal density and leaf length within each species and across the species. While in Central Europe Q. petraea occurs in drier environments than Q. robur, in the present study Q. robur populations grow in more arid environments and have smaller leaves and a higher stomatal density than Q. petraea. Stomatal density had negative correlations with each of the other leaf characters apart from sinus width. In addition, the interspecific PST value (0.48) for stomatal density was relatively high compared to the mean genetic differentiation calculated at eight microsatellite loci (FST = 0.030), suggesting different local adaptations of populations. Further studies that include additional populations will be necessary to associate genetic variation at candidate genes with phenotypic and environmental variation.