Morphological variability of Betula pendula Roth leaves under conditions of technogenic transformation of the environment

The paper analyzes morphological characters variability of Betula pendula Roth leaves growing in the gradient of technogenic soil transformation. Biological material was collected in natural phytocoenoses and in the Pritagilskaya zone of the Middle Urals technogenically contaminated with heavy metals. In the gradient under study, a change in the shape of the leaf blade is observed: it is rounded, the base is straightened and the top is stretched. The sizes of leaf blades of Betula pendula are smaller under conditions of an average level of pollution than in the background and maximum polluted areas. The largest leaves are typical for B. pendula from the most polluted area. In the studied gradient of the technogenic transformation of the environment, four types of leaf blades forms were distinguished: 1) ovate with a rounded-wedge-shaped base and with a pointed apex; 2) triangular-broadly ovate with a rounded-wedge-shaped base and a pointed apex; 3) triangular-broadly ovate with a truncated base and a pointed apex; 4) triangular-broadly ovate with a truncated base and an elongated pointed apex. By the factor analysis the authors have identified the factors that explain 60% of the total variance of the «leaf shape» trait. The variables have large factor loads for the first factor (length and width of the leaf blade, length of the petiole, the distance from the tip of the leaf blade to the widest part) (42%) and smaller loads for the second one (leaf index) (18%). On the basis of these features, a discriminant analysis was carried out, the results of which indicate that the leaves of plants from the impact area differ from the rest. On the basis of the ratio of the general and consistent variability, morphological features were identified that are ecological indicators – the distance between the bases of the first-second and second-third lateral veins of the first order, the distance from the widest part to the base of the leaf blade, IF (shape index sheet). The high overall and low consistent variability of these characteristics is determined to a greater extent by the influence of environmental factors. The analysis of changes patterns in the level of leaves morphological integration in the gradient of soils technogenic transformation showed that Betula pendula is characterized by a protective-stress developmental strategy.