Effects of elevated CO2 concentration on bulbil germination and early seedling growth in Chinese yam under different air temperatures

The present study investigated the effects of elevated carbon dioxide concentration ([CO 2 ]) and air temperature on the germination of seed bulbils and the seedling vigour of two Chinese yam lines. Plants were grown under two [CO 2 ] levels, ambient and elevated (ambient + 200 μmol mol −1 ), and two mean air temperature regimes, 22.2 °C (ambient + 1.4 °C) and 25.6 °C (ambient + 5.2 °C). Elevated [CO 2 ] did not affect bulbil germination under both air temperature regimes. During the early growth stage, the dry weight (DW) of leaves, vines, shoots, roots, belowground parts (roots + tubers) and whole plants were higher under elevated [CO 2 ] than ambient [CO 2 ] for both lines under the low- and high-temperature regimes. The values of vigour indexes (index I = germination % × seedling length and index II = germination % × seedling DW) were also higher under elevated [CO 2 ] than ambient [CO 2 ] for both lines. These results indicated that Chinese yam seedlings respond positively to elevated [CO 2 ] during the early growth stage. The above:belowground DW ratios were lower under elevated [CO 2 ] than ambient [CO 2 ] in seedlings with very small new tubers for both yam lines, indicating that elevated [CO 2 ] strongly affected the root growth in the early growth stage. The DWs of post-treatment seed bulbils were higher in the elevated [CO 2 ] under both air temperature regimes. The results showed that Chinese yam used a smaller amount of the reserves in seed bulbils under elevated [CO 2 ] than under ambient [CO 2 ].