Photosynthesis and photorespiration in soybean [Glycine max (L.) Merr.] chronically exposed to elevated carbon dioxide and ozone

The effects of elevated carbon dioxide (CO2) and ozone (O3) on soybean [Glycine max (L.) Merr.] photosynthesis and photorespiration-related parameters were determined periodically during the growing season by measurements of gas exchange, photorespiratory enzyme activities and amino acid levels. Plants were treated in open-top field chambers from emergence to harvest maturity with seasonal mean concentrations of either 364 or 726 μmol mol-1 CO2 in combination with either 19 or 73 nmol mol-1 O3 (12 h daily averages). On average at growth CO2 concentrations, net photosynthesis (A) increased 56% and photorespiration decreased 36% in terminal mainstem leaves with CO2-enrichment. Net photosynthesis and photorespiration were suppressed 30% and 41%, respectively, by elevated O3 during late reproductive growth in the ambient CO2 treatment, but not in the elevated CO2 treatment. The ratio of photorespiration to A at growth CO2 was decreased 61% by elevated CO2. There was no statistically significant effect of elevated O3 on the ratio of photorespiration to A. Activities of glycolate oxidase, hydroxypyruvate reductase and catalase were decreased 10-25% by elevated CO2, and by 46-66% by elevated O3 at late reproductive growth. The treatments had no significant effect on total amino acid or glycine levels, although serine concentration was lower in the elevated CO2 and O3 treatments at several sampling dates. The inhibitory effects of elevated O3 on photorespiration-related parameters were generally commensurate with the O3-induced decline in A. The results suggest that elevated CO2 could promote productivity both through increased photoassimilation and suppressed photorespiration.

Duke Scholars

Author Chantal D. Reid Environmental Sciences and Policy