Fig. 1 The ¹³C of CO₂ from (a) surface flux, (b) 15-cm depth, and (c) 30-cm depth collected from the replicated FACE experiment in treatment (closed circles, n = 3) and control (open circles, n = 3) plots. Error bars show 1 standard error from the mean. Vertical broken lines show the start of CO₂ fumigation