Abstract
� Greater root production under elevated [CO2] may drive changes in soil C storage and N cycling. However, this depends on root population turnover and chemistry, and the soil depth at which the roots are produced.
� We assessed the effect of elevated [CO2] on root biomass and N inputs at several soil depths using a long-term minirhizotron data set combined with continuous, root-specific measurements of root mass per unit length and [N]. Our experiment was conducted in a Liquidambar styraciflua forest stand exposed to current or elevated atmospheric [CO2] for 9 years.
� CO2-enrichment had no effect on root tissue density or [N] within a given diameter class. Root biomass production, standing crop and mortality were doubled under elevated [CO2]. Over 9 years, root mortality resulted in 681 g m-2 of extra C and 9 g m-2 of extra N input to the soil system under elevated [CO2]. At least half of these inputs were below 30 cm soil depth.
� Quantification of the effects of elevated CO2 on root detritus, especially at depth in the soil, will provide critical information needed for predicting processes such as long-term soil C storage and N cycling.
