PHOTOSYNTHETICA

Photosynthetica 2010, 48(4):507-512 | DOI: 10.1007/s11099-010-0067-7

Variable responses of mesophyll conductance to substomatal carbon dioxide concentration in common bean and soybean

J. A. Bunce^1,*

¹ Crop Systems and Global Change Laboratory, USDA-ARS, Beltsville Agricultural Research Center, Beltsville, USA

Some reports indicate that mesophyll conductance (g _m) to carbon dioxide varies greatly with the substomatal carbon dioxide concentration (C _i) during the measurement, while other reports indicate little or no change in g _m with C _i. I used the oxygen sensitivity of photosynthesis to determine the response of g _m to C _i over the range of about 100 to 300 μmol mol^-1 C _i at constant temperature in common bean (Phaseolus vulgaris) and soybean (Glycine max) grown over a range of temperatures and photosynthetic photon flux densities (PPFD). In soybean grown and measured at high PPFD there was only a slight, approximately 15% decrease in g _m with C _i over the range of 100 to 300 μmol mol^-1. With lower PPFD during the measurement of g _m, and especially with low PPFD during plant growth, there was a larger decrease in g _m with C _i in soybean. In common bean, the same range in C _i resulted in about a 60% decrease in g _m for plants grown and measured at high PPFD, with an even larger decrease for plants at low growth or measurement PPFD. Growth temperatures of 20 to 30°C had little influence on the response of g _m to C _i or its absolute value in either species. It is concluded that these two species differed substantially in the sensitivity of g _m to C _i, and that PPFD but not temperature during leaf development strongly affected the response of g _m to C _i.

Keywords: Glycine max; light; Phaseolus vulgaris; temperature

Received: April 29, 2010; Accepted: August 6, 2010; Published: December 1, 2010Show citation