Abstract:Plant roots act as an important carbon pool, as well as a nutrient pool in terrestrial ecosystems. Roots also provide the main sources of soil C and mineral nutrients. Understanding the effects of elevated CO2 on root C reserve and turnover is necessary to predict the response and feedback of terrestrial ecosystems to global change. This article reviews the responses of root biomass, the quantity and quality of root-derived organic matter, and root turnover rate in grassland ecosystems under the conditions with experimental elevation of air CO2. We conclude that both the direct and indirect effects of CO2 enrichment should be considered when studying the change of carbon allocation among plant organs. Measuring separately the biomass for roots with different functions is recommended to predict precisely the effects of elevated CO2 on the root carbon-reserve. In order to gain more accurate grassland root turnover rate also depends on sorting measured roots by diameter. The C/N of root-derived organic matter generally increases under elevated CO2, but it should be careful to use the C/N only for qualifying carbon decomposition process under elevated CO2. Further studies are needed to clarify the mechanisms controlling the decomposition rate of root litter and organic matter through rhizodeposition.