Ultrastructural and growth responses of young Scots pine seedlings ( Pinus sylvestris) to increasing carbon dioxide and ozone concentrations

Abstract

Three-year-old Scots pine seedlings were exposed to ambient or elevated (2 × ambient) O 3 and CO 2 levels, singly and in combination, during one growth period in open-top field chambers. Growth measurements showed increased shoot length and needle width in response to CO 2 enrichment, whereas O 3 exposure resulted in visible injury (chlorotic mottling and increased yellowing of previous year needles). At the ultrastructural level, O 3 caused increased electron density of chloroplast stroma and increased number of cytoplasmic ribosomes at both CO 2 levels. CO 2 enrichment also resulted in an increase in the size of starch grains in chloroplasts. In general, simultaneous exposure to elevated O 3 reduced the impact of elevated CO 2.