Biomass allocation, needle structural characteristics and nutrient composition in Scots pine seedlings exposed to elevated CO2 and O3 concentrations

Abstract

Three-year-old Scots pine (Pinus sylvestris L.) seedlings were exposed to ambient or elevated ozone (O 3 ) (1.5× ambient) and carbon dioxide (CO 2 ) (590 µmol mol -1 ) concentrations during two growing seasons in open-top field chambers (OTCs). Five different treat- ments were applied in the chambers: filtered air, ambient air, elevated O3, elevated CO2, and elevated O3 and CO2 combined. Ambient plots outside the OTCs were also in- cluded, but the chamber ambient was used as a control in O3 and CO2 treatments due to a significant chamber ef- fect. Increases in yellowing and chlorotic mottling of previous-year (C+1) needles and in the amount of cyto- plasmic ribosomes and electron density of the chloro- plast stroma in current-year (C) and C+1 needle meso- phyll cells were observed in elevated O 3 at both CO 2 concentrations. Elevated O3 alone caused a non-signifi- cant 10.9% decrease in plant total dry mass and a signifi- cant decrease in manganese (Mn) content of C needles. CO2 enrichment caused a significant increase in needle cross-sectional width after the first year of exposure, and an accumulation of starch and slight curling and swelling of the chloroplast thylakoids in the mesophyll tissue of C needles after the second year of exposure. Calcium and Mn contents were increased and copper and nitrogen contents were decreased, significantly, in CO 2-exposed needles. A non-significant 19.1% increase in plant total dry mass was measured in elevated CO 2 alone, whereas a 14.8% reduction in total dry mass, together with a signif- icant reduction in current-year main shoot length, was found in the combined treatment. Overall, in spite of de- creases in O3-induced visible injuries by CO 2, elevated CO 2 levels were not able to counteract the impact of O 3 in this experiment.