Effects of Carbon Dioxide Enrichment on the Metabolism of Soluble Amino Acids and Organic Acids in Barley Primary Leaves.

Responses of soluble amino acids and organic acids to CO2 enrichment were determined with barley primary leaves (Hordeum vulgare L. cv. Brant) grown in controlled environment chambers. Total soluble amino acids were enhanced 33% by CO2 enrichment when determined 9 days after sowing (DAS). However, glutamine and asparagine decreased with advancing leaf age in the elevated CO2 treatment. As a result total soluble amino acids were 59% lower in the elevated (98 Pa) compared to the ambient CO2 (36 Pa) treatment 17 DAS. Extensive chlorosis was observed in the elevated CO2 treatment and this likely impacted soluble amino acid levels in older barley primary leaves. In contrast to the ambient CO2 treatment, glutamine and most other soluble amino acids decreased as much as 60% during the latter half of a 12 h photoperiod in primary leaves of 13 d old seedlings grown under enhanced CO2. Malate was decreased about 9 percent by CO2 enrichment and citrate and succinate were increased by similar amounts when measured 9 and 13 DAS. Therefore, leaf yellowing had much less of an effect on the formation of organic acids than on soluble amino acids. The above results emphasized the sensitivity of N metabolism to CO2 enrichment in barley. A model will be presented describing the impact of elevated CO2 on leaf N components in barley primary leaves. In summary, organic and amino acid levels in barley primary leaves were dynamic and were altered by age, diurnally and in response to CO2 enrichment.