Article,
Increased C availability at elevated carbon dioxide concentration improves N assimilation in a legume.
Plant, cell & environment, 29 (8): 1651--1658 (August 2006)
Abstract
Plant growth is typically stimulated at elevated carbon dioxide concentration (CO2), but a sustained and maximal stimulation of growth requires acquisition of additional N in proportion to the additional C fixed at elevated CO2. We hypothesized that legumes would be able to avoid N limitation at elevated CO2. Soybean was grown without N fertilizer from germination to final senescence at elevated CO2 over two growing seasons under fully open-air conditions, providing a model legume system. Measurements of photosynthesis and foliar carbohydrate content showed that plants growing at elevated CO2 had a c. 25\% increase in the daily integral of photosynthesis and c. 58\% increase in foliar carbohydrate content, suggesting that plants at elevated CO2 had a surplus of photosynthate. Soybeans had a low leaf N content at the beginning of the season, which was a further c. 17\% lower at elevated CO2. In the middle of the season, ureide, total amino acid and N content increased markedly, and the effect of elevated CO2 on leaf N content disappeared. Analysis of individual amino acid levels supported the conclusion that plants at elevated CO2 overcame an early-season N limitation. These soybean plants showed a c. 16\% increase in dry mass at final harvest and showed no significant effect of elevated CO2 on leaf N, protein or total amino acid content in the latter part of the season. One possible explanation for these findings is that N fixation had increased, and that these plants had acclimated to the increased N demand at elevated CO2.
