Photosynthetic response of wheat and sunflower cultivars to long-term exposure of elevated carbon dioxide concentration

Abstract

Wheat (Triticum aestivum L. cv. HD 2329 and DL 1266-5) and sunflower (Helianthus annuus L. cv. MSFH 17 and MRSF 1754) plants were grown in field under atmospheric (360±10 cm3 m-3, AC) and elevated (650±50 cm3 m-3, EC) CO2 concentrations in open top chambers for entire period of growth and development till maturity. Net photosynthetic rate (P N) of wheat cvs. when compared at the same internal CO2 concentration (C i), by generating P N/C i curves, showed lower P N in EC plants than in AC ones. EC-grown wheat cultivars also showed a lesser response to irradiance than AC plants. In sunflower cultivars, P N/C i curves and irradiance response curves were not significantly different in AC and EC plants. CO2 and irradiance responses of photosynthesis, therefore, further revealed a down-regulation of PN in wheat but not so in sunflower under long-term CO2 enrichment. Wheat cvs. accumulated in leaves mostly sugars, whereas sunflower accumulated mainly starch. This further strengthened the view that accumulation of excess assimilates in the leaves under EC as starch is not inhibitory to PN. © 2006 Institute of Experimental Botany, ASCR.