Fig. 3 (a) The ¹³C of soil CO₂ collected from 20-cm depth in the FACE prototype treatment (solid circles) and reference (open circles) plots. The vertical broken lines mark the dates that CO₂ fumigation started for the growing season (on) and stopped for the winter (off). Arrows mark the points used for the calculation of percent live root contribution to soil CO₂. (b) Daily rainfall (mm) measured at Chapel Hill, Orange County, NC (Office of the State Climatologist, North Carolina State University, Raleigh)

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