Responses of a dominant temperate grassland plant (Leymus chinensis) to elevated carbon dioxide and nitrogen addition in China.

The impact of elevated atmospheric CO(2) concentration on plant communities is varied and strongly dependent on the dominant species response, as well as nutrient conditions. Responses of a dominant species (Leymus chinensis) to elevated CO(2) and N application were examined with open-top chambers in a typical temperate grassland in northern China for 3 yr. The significant effect of elevated CO(2) on L. chinensis growth was mainly reflected in the higher photosynthetic rates, increased leaf number, larger shoot and root biomass, and higher root/shoot (R/S) ratio. Enhancement of root biomass induced by elevated CO(2) was larger (40%) than that of shoot biomass (9%). In contrast, N application had a significant impact on most growth indices examined in this study, which was reflected in the enhanced aboveground growth and depressed belowground growth. Nitrogen application significantly reduced the R/S ratio by an average of 40%. Nitrogen addition significantly enhanced the proportion of senescent biomass and decreased the proportion of green leaf biomass under elevated CO(2). There were no CO(2) x N interactions on most of the measured variables, except on photosynthetic rate and the proportion of aboveground biomass. Plant growth variables showed high interannual variation. These results indicate that belowground growth of L. chinensis is more sensitive to elevated CO(2) than is the aboveground. Aboveground growth of L. chinensis is much more sensitive to N application than to CO(2) enrichment. Therefore, the effect of elevated CO(2) on L. chinensis steppe is more likely to be underestimated if only aboveground parts are considered.