Growth adaptability of Norway maple (Acer platanoides L.) to urban environment

Adaptability of Acer platanoides L. to deteriorating urban conditions was assessed through qualitative parameters describing crown destruction, assimilation organs efficiency, chlorophyll a content, and content of alochtonous elements in leaves. The adaptability assessment was based on comparison between study trees growing in an environmentally loaded town area and control trees in a historical rural park, both localities in Slovakia (Central Europe). The results of visual assessments performed in 2015 and 2016 showed higher crown and leaf quality (Qns) for the individuals growing in the rural park (Qns₂₀₁₅ = 0.44, Qns₂₀₁₆ = 0.43) compared to the individuals in urban conditions (Qns₂₀₁₅ = 1.44, Qns₂₀₁₆ = 1.56). The values of chlorophyll a content index (CCI) were higher in the trees growing in the rural park (CCI = 25.914) than in the urban environment (CCI = 16.290). The performance of assimilation organs was evaluated through the maximum fluorescence yield (Fv/Fm) and electron transport rate (ETR) at both sites. During the years 2015 and 2016, there were measured higher values in the rural park (Fv/Fm₂₀₁₅ = 0.828, Fv/Fm₂₀₁₆ = 0.820) than in the town (Fv/Fm₂₀₁₅ = 0.823, Fv/Fm₂₀₁₆ = 0.772). Higher ETR values were measured on trees in the urban area (ETR₂₀₁₅ = 47.345, ETR₂₀₁₆ = 65.284) and lower in the park area (ETR₂₀₁₅ = 36.832, ETR₂₀₁₆ = 59.495). The urban locality demonstrated higher contents of Cu, Zn, Fe, Pb, Na and Ca elements in tree leaves compared to the rural park. The adaptability index (Ia) values indicate an average adaptability of the Norway maple to the urban environment (Ia₂₀₁₅ = 1.93, Ia₂₀₁₆ = 2.13) in comparison with a good adaptability in the rural park (Ia = 0.8–1.6).