Increased C availability at elevated carbon dioxide concentration improves N assimilation in a legume.
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].
Rogers
Alistair
A
Department of Environmental Sciences, Brookhaven National Laboratory, Upton, NY 11973-5000, USA. arogers@bnl.gov
Gibon
Yves
Y
Stitt
Mark
M
Morgan
Patrick B
PB
Bernacchi
Carl J
CJ
Ort
Donald R
DR
Long
Stephen P
SP
D000596:Amino Acids / Q000378:metabolism; D018533:Biomass; D050260:Carbohydrate Metabolism; D002244:Carbon / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology; D018515:Plant Leaves / Q000254:growth & development / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D013025:Glycine max / Q000254:growth & development / Q000378:metabolism*
D000596:Amino Acids; D011506:Proteins; D002245:Carbon Dioxide; D002244:Carbon; D009584:Nitrogen