Soil Contamination by Salinity and Heavy Metals as a Stress Factor in Fraxinus excelsior Saplings Under Natural and Laboratory Conditions

One of the main causes of common ash decline is the impact of heavy metals and salts accumulated in the soil. Furthermore, harmful chemical compounds contribute to the development of abnormalities in the morphogenesis of plant cells. Studies in natural conditions (in vivo) were conducted to select common ash populations with the highest resistance to salts (NaCl) at varying concentrations and heavy metals such as zinc (Zn), cadmium (Cd), and chromium (Cr). The studies were conducted to facilitate the precise and rapid assessment of the harmful substances impact on the plants health from a given population. Saplings from three populations originating from different geographical and climatic regions in southern and southeastern Poland. To ensure the full multidimensionality of the studies, experiments were also conducted under controlled laboratory conditions (in vitro). The in vitro seedlings grown under sterile conditions, served as a reference pattern with the best physiological. The in vitro plants were used for comparison with saplings grown in vivo. To determine the effect of selected abiotic factors on the saplings, measurements were taken of chlorophyll fluorescence parameters, the maximum quantum yield of photosystem II (Fv/Fm), the maximum efficiency of the water-splitting complex on the donor side of PSII (Fv/Fo), and the time to reach maximum chlorophyll fluorescence (Tfm) for both in vivo and in vitro plants. The studies showed that the values of the parameters studied varied depending on the geographical origin of the studied populations. The analyses of the Fv/Fm and Fv/Fo parameters of individual ash populations showed that the in vivo saplings population from southeastern Poland had the lowest resistance to Zn and Cd. In turn, Zn was the compound that caused the greatest disruptions in Fv/Fm and Fv/Fo functioning in in vivo saplings across all the studied populations. The analysis of the Tfm parameter showed that all toxic substances significantly affected the development of disturbances in the photosynthetic system of all saplings populations examined. The obtained results will help foresters in breeding healthy and resistant saplings and increasing the species population using both in vivo and in vitro methods, taking into account the influence of climate on resistance and the development of adaptive capacity of common ash saplings to the effects of soil contamination.