Effects Of Elevated CO₂ Concentration On Contents And Allocation Of Carbohydrates In Betula Albosinensis (Burk.) Seedlings

Carbohydrates found in plants are frequently grouped into two different classes:structural carbohydrates and non-structural carbohydrates. The former mainlyconstruct the plant basic framework, while the latter are essential for plant growth andmetabolism. As yet there is lack of information on the effects of elevated CO₂concentration on carbohydrate contents in stem, branch and root of plant, and oncarbohydrate allocation in organs of plant although there have been many reports onthe responses of carbohydrate contents to elevated CO₂ concentration in plant foliages.A shift of carbohydrate contents in plant reflects a change in transporting ofphotosynthetic production from leaf to stem, branch and root of plant. The allocationof carbohydrates that is correlated to plant growth patterns affects plant growth. Thus,in order to understand the influences of elevated CO₂ on biochemical process,physiological change and plant growth well, the response of carbohydrate contentsand allocation in plant to elevated CO₂ should be further investigated. In our study, theeffects of elevated CO₂ on carbohydrate contents and their allocation between leaf,stem, branch and root tissue of Betula albosinensis seedlings were determined. Theseedlings were grown in independent and enclosed-top chambers. Chambers werecontrolled to reproduce ambient (CK) and ambient + 350μmol·mol^-1 CO₂ (EC)concentration for 1 year. The results here showed that,1) Elevated CO₂ significantly increased non-structural carbohydrate contents in leafof red birch seedlings. This will reduce photosynthetic rate. 2) Elevated CO₂ also significantly increased non-structural carbohydrate contentsin root, stem and branch of red birch seedlings. These findings supported thehypothesis that elevated CO₂ accelerated carbohydrates from leaf to branch, stem androot.3) Starch makes up the largest parts of total non-structural carbohydrate. In thesame way, the increase of starch plays a main role in the increase of totalnon-structural carbohydrate under elevated CO₂. In leaf, branch, stem and root, theincrements of starch contents comprised 91.45%, 88.23%, 83.23% and 82.01% of theincrements of total non-structural carbohydrate contents.4) Under elevated CO₂ the cellulose contents have an increasing tendency in redbirch seedlings. It is needed to investigate the effects of long-term elevated CO₂ oncellulose contents in plant.5) There are significant CO₂ effects on the allocation of carbohydrate in organs ofred birch seedlings. Under elevated CO₂ more carbohydrates were allocated to root.Moreover, CO₂ enrichment significantly increased the root to shoot ratio of red birchseedlings and the dry weight of roots. These results supported Gorissen and Cotrufo'shypothesis that increase of carbohydrate allocation to root mostly contributed to theincrease of root to shoot ratio.6) Elevated CO₂ brought about a reduction in the nitrogen contents of leaf, stem,branch and root. The decline of nitrogen contents under elevated CO₂ is mainlycaused by the dilution effects of increasing starch level and growth of red birchseedlings.