Photosynthesis, fluorescence, and biomass responses of white oak seedlings to urban soil and air temperature effects.

Urban forest patches can provide critical ecosystem services and their ability to regenerate native tree species is critical to their sustainability. Little is known about native tree seedling establishment and physiological function in urban ecosystems. This growth chamber study examined the effects of urban soil and air temperatures on white oak (Quercus alba L.) germination, seedling growth, and leaf-level physiology. A split-plot design tested effects of field collected soils from urban and reference forest sites in Baltimore, Maryland, and warm (urban) versus cool (rural) growth chamber temperature regimes. Seedlings were harvested at the end of the 23-week experiment to assess foliar chemistry and biomass allocation. Seed germination was unaffected by treatments and was high in both soil types and temperature regimes. Urban soils supported significantly higher total seedling biomass and had a significant effect on leaf-level physiological parameters, with seedlings grown in urban soils having greater Anet , Vcmax , ETRmax , Jmax , PNUE, gs , Anet /Rd , and PIabs (an integrated chlorophyll fluorescence parameter). PIabs measurements taken throughout the experiment revealed a significant time × temperature interaction effect. Baltimore urban forest patch soils were higher in nutrients than reference soils, but also higher in heavy metals. Despite higher levels of heavy metals, these results demonstrate that urban forest patch soils are able to support robust white oak seedling growth and enhanced seedling physiological parameters. However, interactions with temperature suggest that warming air temperatures may cause seedling stress and reduced growth.