Impact of elevated O3 on visible foliar symptom, growth and biomass of Cinnamomum camphora seedlings under different nitrogen loads

Abstract

The effects of elevated ozone (O₃) and enhanced nitrogen (N) on the growth and biomass of Cinnamomum camphora, a subtropical evergreen broad-leaved tree species, were investigated. The seedlings, supplied with N (NH₄NO₃ solution) at 0, 30 and 60 kg ha⁻¹ year⁻¹ (simplified as N0, N30, N60, respectively), were exposed to ambient (AA) or elevated O₃ (AA + 60 nmol mol⁻¹ and AA + 120 nmol mol⁻¹, designated as AA + 60 and AA + 120, respectively) for the 2009 and 2010 growing seasons. Symptomatic leaf percentages were significantly increased with O₃ concentration. AA + 120 significantly decreased the mean leaf size and chlorophyll content of both 2009- and 2010-emerged leaves, inhibited the growth of stem height and basal diameter, and reduced biomass accumulation of all plant parts except for leaves. By comparison, only the chlorophyll content of 2009-emerged leaves and root dry weight were significantly reduced under AA + 60. Specific leaf area, total leaf area and foliar biomass were not affected even at a higher O₃ level. On the other hand, N loads, especially N60, exerted significantly positive effects on all variables except mean leaf size and shoot/root ratio. No significant interactions between O₃ and N were detected, suggesting that the N supply at ≤60 kg ha⁻¹ year⁻¹ did not significantly modify the response of C. camphora to O₃ in terms of seedling growth and biomass accumulation.