Photosynthesis by White Clover Leaves in Mixed Clover/Ryegrass Swards

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Abstract
Measurements of rates of net photosynthesis were made on single Blanca white clover leaves on plants taken from a field-grown, mixed clover/perennial ryegrass sward during two regrowth periods. Net photosynthesis fell by 20 per cent in the first measurement period as leaf area index increased and the grass component of the crop flowered, but did not change significantly in the second measurement period during which the grass remained vegetative. Leaves which had been artificially protected from shading in the sward did not have significantly different photosynthetic capacities from leaves in the undisturbed sward, even in the first measurement period. As leaf area index and sward height increased, successive clover petioles were longer, keeping the newly expanded leaves near the top of the sward where they received full light. It is suggested that it is this which allows successive clover leaves, unlike those of vegetative grasses, to attain a high photosynthetic capacity throughout a growth period.