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 gr ound in open top chambers and exposed to two concentrations of atmospheric CO2 (ambient or ambient + 400 mu mol mol(-1)) without addition of nutrients and water. Biomass production (above-ground and below-ground) and allocati on, as well as canopy structure and tissue nitrogen concentrations and cont ents, were examined by destructive harvest after 3 years. Elevated CO2 incr eased 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 root s under elevated CO2 The proportion of dry matter in roots was increased by elevated CO2, as indicated by increased root-to-shoot ratio and root mass ratio. Within the root system, there was a significant shift in the allocat ion towards fine roots. Root litter constituted a much higher fi action of fine roots in trees grown in the elevated CO2 than in those grown in ambien t CO2. Growth at elevated CO2 caused a significant decline in nitrogen conc entration only in the needles, while nitrogen content significantly increas ed in branches and fine roots (with diameter less than 1 mm). There were no changes in crown structure (branch number and needle area distribution). B ased upon measurements of growth made throughout the 3 years, the greatest increase in biomass under elevated CO, took place mainly at the beginning o f the experiment, when trees grown in elevated CO2 had higher relative grow th rates than those grown under ambient CO2; these differences disappeared with time. Symptoms of acclimation of trees to growth in the elevated CO2 t reatment were observed and are discussed. (C) 2000 Annals of Botany Company .