Responses of nitrogen metabolism in N-sufficient barley primary leaves to plant growth in elevated atmospheric carbon dioxide

Effects of atmospheric carbon dioxide enrichment on nitrogen metabolism wer e studied in barley primary leaves (Hordeum vulgare L. cv. Brant). Seedling s were grown in chambers under ambient (36 Pa) and elevated (100 Pa) carbon dioxide and were fertilized daily with complete nutrient solution providin g 12 millimolar nitrate and 2.5 millimolar ammonium. Foliar nitrate and amm onium were 27% and 42% lower (P less than or equal to 0.01) in the elevated compared to ambient carbon dioxide treatments, respectively. Enhanced carb on dioxide affected leaf ammonium levels by inhibiting photorespiration. Di urnal variations of total nitrate were not observed in either treatment. To tal and Mg2+ inhibited nitrate reductase activities per gram fresh weight w ere slightly lower (P less than or equal to 0.01) in enhanced compared to a mbient carbon dioxide between 8 and 15 DAS. Diurnal variations of total nit rate reductase activity in barley primary leaves were similar in either tre atment except between 7 and 10 h of the photoperiod when enzyme activities were decreased (P less than or equal to 0.05) by carbon dioxide enrichment. Glutamate was similar and glutamine levels were increased by carbon dioxid e enrichment between 8 and 13 DAS. However, both glutamate and glutamine we re negatively impacted by elevated carbon dioxide when leaf yellowing was o bserved 15 and 17 DAS. The above findings showed that carbon dioxide enrich ment produced only slight modifications in leaf nitrogen metabolism and tha t the chlorosis of barley primary leaves observed under enhanced carbon dio xide was probably not attributable to a nutritionally induced nitrogen limi tation.