EFFECT OF LIGHT INTENSITY DURING GROWTH ON LEAF ANATOMY AND SUBSEQUENT LIGHT-SATURATED PHOTOSYNTHESIS AMONG CONTRASTING LOLIUM GENOTYPES

The effect of light intensity during leaf formation on subsequent light‐saturated photosynthesis and its relation to mesophyll and stomatal characteristics, was examined among ten contrasting Lolium genotypes. Photosynthetic activity was recorded at three CO2 concentrations. At approximately 300 ppm CO2 and above, plants of the same mesophyll cell size grown in strong light (0.130 cal/cm2/min) of radiation in the spectral region 400–720 mμ. (1800 ft‐candles) had faster rates of photosynthesis than those grown in relatively weak light (0.021 or 0.056 cal/cm2/ min). At the lowest CO2 concentration there was no effect on photosynthesis of the light intensity at which the plants were grown. The effect of light intensity was not associated with any change in mesophyll structure, but plants grown in weaker light (0.056 cal/cm2/min) had much smaller stomata than those grown in stronger light (0.130 cal/cm2/min). A slight increase in stomatal frequency at the low compared with the high light intensity did not compensate for the reduced stomatal length in terms of total pore space. Differences in apparent photosynthesis in any one light intensity, and between plants from all light intensities at the lowest CO2 concentration, were usually correlated negatively with mesophyll cell size. Effects of the light intensity at which plants were grown on subsequent photosynthesis could be explained in terms of changes in stomatal size. Copyright © 1969, Wiley Blackwell. All rights reserved