Fig. 7. Rice root biomass (top panel) and root length density (bottom panel) at 5-cm depth increments sampled at 70 d after planting from a cluster of four plants growing in 20-cm-diameter cylindrical pots in the Soil–Plant–Atmosphere Research (SPAR) chambers at two CO₂ concentrations and three temperature regimes. Values for 330 µmol mol^-1 in solid bars are plotted over values for 660 µmol mol^-1 in hatched bars. Across three samplings during the season, root length density (cm cm^-3) at the 0- to 5-cm soil depth = 0.264 + 4.32 x root biomass (g); r² = 0.99.