Growth Response of Orchardgrass (<i>Dactylis glomerata</i> L.) to Different Light and Temperature Environments. II. Leaf Age and Photosynthetic Activity¹

Abstract

The variation in rate of apparent photosynthesis (PR) with leaf age in three populations of orchardgrass, grown in two different temperature environments, was investigated using a Warburg manometric technique. Fully expanded leaves maintained a high PR for 15 to 20 days but the rate rapidly declined thereafter. PR (oxygen evolution) per unit leaf area closely paralleled the synthesis and degradation of the chlorophyll pigments; PR per unit chlorophyll changed very little throughout the life of the leaf. These results were confirmed by the pattern of assimilation of C 14 O 2 by leaves of different ages. The Portuguese ecotype had a significantly higher photosynthetic rate at 21 C than the cultivars ‘S.143’ and ‘Boone’ in both growth environments. Plants grown at 21 C day/13 C night temperatures had a significantly higher rate at 21 C than plants grown at 29 day/21 night temperatures, but when measured at 29 C plants grown in the higher temperature regime had a significantly higher rate of PR. The relative pattern of change of PR with leaf age was unaffected by the temperature at which the plants were grown.