Carbon allocation, root exudation and mycorrhizal colonization of Pinus echinata seedlings grown under CO(2) enrichment.

Increased exudation of carbon compounds from roots may provide a mechanism for enhancement of nutrient availability to plants growing in a CO(2)-enriched atmosphere. Therefore, the effect of atmospheric CO(2) concentration on carbon allocation and root exudation was investigated in Pinus echinata Mill. (shortleaf pine) seedlings. After 34 and 41 weeks, seedlings growing in 695 microl l(-1) CO(2) allocated proportionately more (14)C-labeled photosynthate to fine roots than did seedlings growing in ambient air. This was associated with greater fine root mass and mycorrhizal density in CO(2)-enriched plants after 34 weeks. Exudation of soluble, (14)C-labeled compounds from roots also was greater in these plants at 34 weeks, but the effect of CO(2) concentration on exudation did not persist at 41 weeks.