Fig. 4. Average (a) root intensity and (b) root frequency in the 0- to 2.42-m soil profile before the start of the ¹⁵N injection experiment; and (c) plant ¹⁵N uptake during the 6-d ¹⁵N injection experiment starting 25 October. Notice the break on the x-axis. Part (d) shows NO₃ concentrations in the 0- to 2.5-m soil profile. The error bars indicate standard errors (n = 4).