Responses of typical plant functional traits among summer-flowering tree species in heterogeneous city habitats in Lanzhou City of northwestern China

Objective This study probed into the differences and associated features of functional traits among summer-flowering tree species growing in heterogeneous urban habitats, then recognized which factors influenced the functional traits’ performances.

Method Five summer-flowering tree species, i.e Sophora japonica, Koelreuteria paniculata, Sambucus williamsii, Aesculus chinensis and Sorbaria kirilowii, which were widely applied in three typical road habitats and three residential habitats in Lanzhou urban area of northwestern China, were selected to sample and measure their leaf functional traits in summer, 2020. Also, these sampled trees were marked to determine their reproductive functional traits during the full-bloomimg and full-fruiting period. Correlation analysis was applied to make a thorough inquiry of the relationship between environmental factors and tree species’ functional traits, and path analysis was used to explore the correlations between leaf functional traits and various reproductive functional traits.

Result Compared with residential habitat, species growing in road habitat showed a lower value of flowering number, inflorescence length, inflorescence axis diameter and seed setting rate, while leaf dry mass per area, leaf dry matter content, leaf tissue density and leaf thickness increased. In addition, leaf area reduced and duration of green foliage was shorter. According to correlation analysis, there existed the significant or the most significant correlations between part of leaf functional traits and reproductive functional traits. Correlations between soil conditions, most inflorescence traits and leaf functional traits were significant or the most significant. As for major atmospheric pollutants, the correlations between O₃ concentrations, most inflorescence traits and leaf traits were significant or the most significant. Path analysis indicated that the performance of each reproductive functional trait was affected by multiple leaf functional traits. In road habitat, leaf dry mass per area, leaf thickness and leaf tissue density had a significant effect on reproductive functional traits, while in residential habitat, the effects were not significant, thus summer-flowering tree species’ strategies to resource utilization were different in various urban habitats.

Conclusion Five summer-flowering tree species differently change their functional trait performance in road and residential habitats in urban areas. Differences of soil conditions and atmospheric pollutant levels in two habitats are closely related to tree species’ functional trait performances. Among five summer-flowering tree species, leaf functional traits could togetherly affect reproductive functional traits, strategies to resource utilization among tree species are not identical in various urban habitats.