Photosynthesis of White Clover Leaves as Influenced by Canopy Position, Leaf Age, and Temperature

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Abstract
Microswards of white clover (Trifolium repens L.) were grown in controlled environments at 10/7, 18/13 and 26/21 °C day/night temperatures. The vertical distribution of leaves of different ages and their rates of 14CO2-uptake in situ were studied. Extending petioles carried the laminae of young leaves through the existing foliage. A final position was reached within 1/4 to 1/3 of the time between unfolding and death. Newly unfolded leaves had higher rates of 14CO2-uptake per leaf area than older ones at the same height in the canopy. At higher temperatures, the decrease with age was faster. However, the light-photosynthesis response of leaves which were removed from different heights in the canopy varied much less with leaf age than did the rates of 14CO2-uptake in situ. The comparison of the rates of 14CO2-uptake in situ with the light-photosynthesis response curves suggests that young leaves receive more light than older ones at the same height in the canopy. This would imply that young white clover leaves have the ability to reach canopy positions having a favourable light environment. This ability may improve the chances of survival of white clover in competition with other species.