The effects of elevated carbon dioxide concentration on the morphology of leaf blades in two Chinese yam lines under different temperature conditions were determined. Plants were grown under two [CO_(2)] levels, ambient (about 400?μmol mol~(?1)) and elevated (ambient +?200?μmol mol~(?1)) in the daytime, and two mean air temperature regimes, approximately ambient temperature (22.2°C) and high temperature (25.6°C). The palisade layer was thicker under elevated [CO_(2)] than under ambient [CO_(2)] in both temperature regimes, and the whole yam leaf blade was thicker under elevated [CO_(2)] than under ambient [CO_(2)] in the approximately ambient temperature regime. The numbers of chloroplasts per palisade cell and spongy cell as well as per unit profile area of palisade cell, number of starch grains per chloroplast, profile area of the starch grain, and starch-to-chloroplast area ratio in both palisade and spongy cells were higher under elevated [CO_(2)] than under ambient [CO_(2)] in both temperature regimes. Furthermore, the stomatal density on the abaxial side of the leaf blade in Chinese yam was greater under elevated [CO_(2)] than under ambient [CO_(2)] under both temperature regimes, and stomatal-pore length was higher under elevated [CO_(2)] than under ambient [CO_(2)] in the approximately ambient temperature regime. These results indicate that elevated [CO_(2)] positively affects the photosynthetic apparatus. The results of this study provide information for understanding the response characteristics of the leaf blade under elevated [CO_(2)] and a possible explanation for the positive photosynthetic responses of Chinese yam to elevated [CO_(2)] in our previous study.
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