Microclimate, Canopy Structure and Photosynthesis in Canopies of Three Contrasting Temperate Forage Grasses: III. Canopy Photosynthesis, Individual Leaf Photosynthesis and the Distribution of Current Assimilate

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Abstract
The rates of canopy and individual leaf photosynthesis and 14C distribution for three temperate forage grasses Lolium perenne cv. S24, L. perenne cv. Reveille and Festuc'a arundinacea cv. SI70 were determined in the field during a summer growth period. Canopy photosynthesis declined as the growth period progressed, reflecting a decline in the photosynthetic capacity of successive youngest fully expanded leaves. The decline in the maximum photosynthetic capacity of the canopies was correlated with a decline in their quantum efficiencies at low irradiance. Changes in canopy structure resulted in changes in canopy net photosynthesis and dark respiration. No clear relationships between changes in the environment and changes in canopy net photosynthesis and dark respiration were established. The relative distributions of 14C in the shoots of the varieties gave a good indication of the amount of dry matter per ground area in the varieties.