Anatomical and morphological changes in Pinus sylvestris and Larix sibirica needles under impact of emissions from a large aluminum enterprise

Species-specific anatomical and morphological characteristics of Pinus sylvestris and Larix sibirica needles were studied at different levels of tree stand pollution by aluminum smelter emissions. The anatomical characteristics of the needle were studied using light microscopy. The level of tree stand pollution was determined using the cluster analysis outcomes of the pollutant elements content (fluorine, sulfur, and heavy metals) in the needles. Four levels of tree stand pollution were separated: low, moderate, high, and critical, as well as background tree stand in unpolluted areas. It was found that the state of tree phytomass deteriorated with increasing levels of pollution (from low to critical): pine crown defoliation increased to 85%, and larch defoliation increased to 65%. The life span of pine needles was reduced to 2–3 years, with a background value of 6–7 years. The change of morphological parameters was more pronounced in P. sylvestris: the weight and length of the 2-year-old shoot decreased by 2.7–3.1 times compared to the background values; the weight of needles on the shoot and the number of needle pairs on the shoot—by 1.9–2.1 times. The length of the needle and shoot and the number of L. sibirica brachyblasts decreased by 1.8–1.9 times. The anatomical parameters of the needle also changed to a greater extent in P. sylvestris . Up to the high level of tree pollution, we observed a decrease in the cross-sectional area of the needle, central cylinder, vascular bundle, area and thickness of mesophyll, number and diameter of resin ducts by 18–66% compared to background values. At the critical pollution level, when the content of pollutant elements in pine needles reached maximum values, the anatomical parameters of the remaining few green needles were close to background values. In our opinion, this may be due to the activation of mechanisms aimed at maintaining the viability of trees. A reduction in thickness and area of assimilation tissue in the L. sibirica needle was detected only at the critical pollution level. An upward trend in these parameters was found at low, medium, and high pollution levels of tree stand, which may indicate an adaptive nature. The results suggested that at a similar pollution level of trees, the greatest amount of negative anatomical and morphological changes were recorded in pine needles, which indicates a greater sensitivity of this species to technogenic emissions.