Seasonal Changes in the Physiology of S24 Perennial Ryegrass (Lolium perenne L.)

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Abstract
Measurements of CO2 exchange were used to construct a detailed account of the carbon economy of established simulated swards of perennial ryegrass during 10 week periods in spring and autumn. Changes in sward dry weight estimated from gas exchange measurements closely matched observed changes in dry weight. In spring, light energy increased, the photosynthetic potential of the canopy increased, and together these factors led to a pattern of increasing photosynthetic uptake. In autumn, decreasing light energy and decreasing canopy photosynthetic potential led to decreasing photosynthetic uptake. During the periods investigated, the changes in light energy receipt played the major role in determining the pattern of photosynthetic uptake. A simple model of crop growth was used to illustrate the effect of such characteristic seasonal differences in the pattern of photosynthetic uptake on the subsequent loss of carbon during respiration and tissue death, and consequently on the production of live tissue. The model describes how a reproductive crop in spring may accumulate more living dry matter than a vegetative crop in autumn from the same total gross photosynthetic uptake of carbon.

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