Effect of elevated CO₂ concentration on carbohydrate and nitrogen contents in seedlings foliage of three tree species in Changbai Mountain

The contents of sucrose, fructose, soluble total sugar, starch and total nitrogen were analyzed in seedlings of Pinus koraiensis, Pinus sylvestriformis and Fraxinus mandshurica grown for three growing seasons in open-top chambers in Changbai mountain under elevated CO₂ (700, 500 μmol·mol^-1) and ambient CO₂ (350 μmol·mol^-1) concentrations. The results showed that in the first two growing seasons the treatment of 700 μmol·mol^-1 CO₂ accumulated the contents of starch in Pinus sylvestriformis and Fraxinus mandshurica seedlings, while total nitrogen content significantly decreased in Pinus koraiensis seedlings under 700 and 500 μmol·mol^-1 CO₂. The content of starch increased and the content of total nitrogen decreased in Pinus koraiensis and Fraxinus mandshurica seedlings grown under 700,500 μmol·mol^-1 CO₂ at the first two weeks in the third growing season. The change of starch and total nitrogen in Fraxinus mandshurica at the eighth week was similar to the first and second week. There was no significant increase or decrease of C and N content in Pinus sylvestriformis at the third growing season. CO₂ concentration affected the forms of carbohydrate accumulation in foliage.