Growth, respiration and nitrogen content in needles of Scots pine exposed to elevated ozone and carbon dioxide in the field

Abstract

Single Scots pine ( Pinus sylvestris L.) trees, aged 30 years, were grown in open-top chambers and exposed to two atmospheric concentrations of ozone (O 3; ambient and elevation) and carbon dioxide (CO 2) as single variables or in combination for 3 years (1994–1996). Needle growth, respiration and nitrogen content were measured simultaneously over the period of needle expansion. Compared to ambient treatment (33 nmol mol −1 O 3 and 350 μmol mol −1 CO 2) doubled ambient O 3 (69 nmol mol −1) significantly reduced the specific growth rates (SGRs) of the needles in the early stage of needle expansion and needle nitrogen concentration ( N 1) in the late stage, but increased apparent respiration rates (ARRs) in the late stage. Doubled ambient CO 2 (about 650 μmol mol −1) significantly increased maximum SGR but reduced ARR and N 1 in the late stage of needle expansion. The changes in ARR induced by the different treatments may be associated with treatment-induced changes in needle growth, metabolic activities and turnover of nitrogenous compounds. When ARR was partitioned into its two functional components, growth and maintenance respiration, the results showed that neither doubled ambient O 3 nor doubled ambient CO 2 influenced the growth respiration coefficients ( R g). However, doubled ambient O 3 significantly increased the maintenance respiration coefficients ( R m) regardless of the needle development stage, while doubled ambient CO 2 significantly reduced R m only in the late stage of needle expansion. The increase in R m under doubled ambient O 3 conditions appeared to be related to an increase in metabolic activities, whereas the decrease in R m under doubled ambient CO 2 conditions may be attributed to the reduced N 1 and turnover rate of nitrogenous compounds per unit. The combination of elevated O 3 and CO 2 had very similar effects on growth, respiration and N 1 to doubled ambient O 3 alone, but the interactive mechanism of the two gases is still not clear.