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Fig. S1 Increasing CO2 by 200 μl l−1 lowers the δ13C of the CO2 in the elevated FACE plots to –20‰.

Fig. S2 Isotopic composition of fumigation CO2 at the Duke FACE site.

Fig. S3 Pool size isotope correction for estimating fluxes from pool residence times that was applied to live and dead roots of different diameter classes and soil CO2.

Fig. S4 Model for correcting incorporation of post-treatment C in root decomposition.

Fig. S5 Soil respiration for the elevated plots as simulated by Hui and Luo (2004).

Fig. S6 Cluster profile plots from the k-means analysis demonstrate that GPP is primarily responsible for the clustering, and root respiration rate is not.

Fig. S7 Daily GPP versus the day of year partitioned into two clusters using k-means cluster analysis.

Fig. S8 Daily current-year C utilized for root respiration versus the day of year.

Table S1 Isotope end-members for calculations of pretreatment C (A, ambient) and post- treatment C (E, elevated) at the Duke FACE site

Table S2 Averaged monthly values of the proportion of current photosynthate (% new C) respired by soils that was not originated in decomposition of leaf and root litter pools

Table S3 Partitioning of GPP into ecosystem components and fluxes at the Duke FACE site

Table S4 Summary statistics for k-means clustering analysis

Notes S1 Contribution of current photosynthate to root-rhizosphere respiration.