Nitrogen budget under elevated CO(sub 2) levels: regulation by absorption and assimilation

摘要

The focus of this research was to investigate plant nitrogen budget under elevated CO(sub 2) concentration. Of particular interest were the following: (1) Does elevated CO(sub 2) increase root carbohydrate availability. (2) Does such an enhancement increase kinetics of root nitrogen acquisition. (3) Does the effect on kinetics differ between NH(sub 4)(sup+) and NO(sub 3)(sup -). (4) If there are interspecific differences in (1)-(3), could those variations lead to changes in community composition. This report shows that, although root carbohydrate availability often increases in response to elevated CO(sub 2), such an increase is neither necessary nor directly related to changes in root N uptake kinetics . The data also show that, depending on species, the effects of elevated CO(sub 2) on root nitrogen uptake kinetics ranges from down regulation to no changes to up regulation. Furthermore, the effects on NH(sub 4)(sup+) are not always similar to the effects on NO(sub 3)(sup -). It is concluded that elevated CO(sub 2) can have a dramatic effect on root N uptake kinetics, but viewed in isolation this observation does not provide a robust assessment of plant N economy under an enriched CO(sub 2) atmosphere. Therefore, future work designed to predict whole-plant N responses to elevated CO(sub 2) must consider other root system adjustment s listed above, collectively.