Changes of Cinnamomum camphora root characteristics and soil properties under ozone stress in South China

High O₃ exposure affects the forest growth and soil characteristics. Although there is substantial evidence that O₃ does impose a stress on forest trees, the effects of O₃ on roots and soil of evergreen broad-leaved tree species in South China remain unknown. The effects of ozone (O₃) fumigation on the root biomass, root morphology, root nutrient, soil physical, and chemical properties were examined in Cinnamomum camphora seedlings grown under four O₃ treatments (charcoal-filtered air (CF) or O₃ at 1×, 2× and 4× ambient concentration). O₃ significantly decreased root biomass and root carbon (C). Regardless of O₃ level, elevated O₃ significantly resulted in reduced root surface area, volume, number of forks, and specific root length (SRL). The percentages of fine to total root in terms of root surface area and root volume of seedlings under the CF and 1 × O₃ treatments were significantly higher than those of seedlings under the 4 × O₃ treatment, indicating that high O₃ level impaired the growth performance of fine roots. O₃ affected root growth and structures, which increased soil bulk density and reduced soil total porosity and void ratio. The soil pH under all O₃ fumigation treatments significantly increased compared with CF treatment, whereas the organic matter significantly decreased. In conclusion, although the increased O₃ level enhanced root N and P under 2 and 4 × O₃ treatments compared with 1 × O₃ treatment as compensation mechanisms to prevent O₃-induced decrease in root C gain and root functions, O₃ still decreased the root biomass and root tips, and changed the soil physical and chemical properties.