Above- and Below-ground Production of Young Scots Pine (Pinus sylvestris L.) Trees after Three Years of Growth in the Field under Elevated CO2

Scots pine ( Pinus sylvestris L.) seedlings were grown for 3 years in the ground in open top chambers and exposed to two concentrations of atmospheric CO 2 (ambient or ambient + 400 μ mol mol −1 ) without addition of nutrients and water. Biomass production (above-ground and below-ground) and allocation, as well as canopy structure and tissue nitrogen concentrations and contents, were examined by destructive harvest after 3 years. Elevated CO 2 increased total biomass production by 55%, reduced needle area and needle mass as indicated, respectively, by lower leaf area ratio and leaf mass ratio. A relatively smaller total needle area was produced in relation to fine roots under elevated CO 2 . The proportion of dry matter in roots was increased by elevated CO 2 , as indicated by increased root-to-shoot ratio and root mass ratio. Within the root system, there was a significant shift in the allocation towards fine roots. Root litter constituted a much higher fraction of fine roots in trees grown in the elevated CO 2 than in those grown in ambient CO 2 . Growth at elevated CO 2 caused a significant decline in nitrogen concentration only in the needles, while nitrogen content significantly increased in branches and fine roots (with diameter less than 1 mm). There were no changes in crown structure (branch number and needle area distribution). Based upon measurements of growth made throughout the 3 years, the greatest increase in biomass under elevated CO 2 took place mainly at the beginning of the experiment, when trees grown in elevated CO 2 had higher relative growth rates than those grown under ambient CO 2 ; these differences disappeared with time. Symptoms of acclimation of trees to growth in the elevated CO 2 treatment were observed and are discussed.