Two-year-old Sitka spruce (Picea sitchensis (Bong.) Carr.) plants were initially grown in standard potting compost (peat, sand and grit) and placed in open-top chambers for 2 years at either ambient (350 ppm) or ambient + 350 ppm CO2 concentration. After four years the plants were removed from the pots and planted directly into the forest soil of same-designed open-top chambers with the randomized treatments in terms of CO2, nutrition and aspect for the extra 2 years. Each chamber was divided into four equal quadrants in which half of quadrants received full strength nutrient solution (70 kg ha1 N) and the remaining half received water only. The mean tree height and basal diameter responded positively to CO2 enrichment and nitrogen supply. The fresh mass, dry mass, width, thickness and leaf area of two-year-old needles were found to increase in elevated CO2 and N supply, but there was no change in needle length. Elevated CO2 had no effect on one-year-old and current needles, but there was an effect of added N on their fresh mass and dry mass. The foliar concentrations and contents of N and P were lower in elevated CO2, but showed a positive response on N supply during the growing season. Elevated CO2 resulted in higher foliar C:N ratios of all ages, but to a certain degree this was offset by added N. The effect of elevated CO2 on foliar C:N ratio was more pronounced in one-year-old and two-year-old needles than in the current needles. The foliar nutrient concentrations decreased might be due to the increase in foliar dry mass through the increased foliar starch accumulation in elevated CO2. There were inconsistent changes in N and P fluxes in the needles in opposite directions was found.
Key words: Sitka spruce, CO2 enrichment, nitrogen supply, growth, foliar nutrient concentration.
Correspondence: Shirong Liu, Institute of Ecology and Resource Management, University of Edinburgh, King's Buildings, Darwin Building, Mayfield Road, EH9 3JU, Edinburgh, United Kingdom