Leaf Anatomy of Four Species Grown under Continuous CO2Enrichment

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Abstract
The effects of continuous, atmospheric CO2 enrichment on leaf anatomy and morphology were examined for corn (Zea mays L. ''Golden Bantam''), soybean (Glycine max [L.] Merrill ''Ransom''), loblolly pine (Pinus taeda L.), and sweet gum (Liquidambar styraciflua L.). Plants were exposed to constantly monitored CO2 levls of 340, 520, 718 and 910 ppm throughout the growing season in the field. Samples obtained from fully expanded leaves were subjected to routine anatomical procedures, sectioned transversely at 10 .mu.m, and measured for total thickness and thicknesses of epidermal, palisade, and spongy mesophyll layers. Epidermal peels and scanning electron microscopy were used to observe possible changes in leaf surfaces. Significant increases were measured in leaf thickness for the 3 C3 species under enriched CO2 conditions, but not for corn, a C4 plant. The influence of CO2 treatments on changes in stomatal indices was not significant, and there were no clear patterns in variation in stomatal frequency among treatments. Chloroplasts in leaf tissues of plants from CO2-enriched treatments appeared denser and were more deeply stained by the crystal violet.