Figure 2.

Relationships between N concentration and root age in P. tremuloides as affected by the N supply level. (a) Roots from the second sampling in the field experiment. (b) The greenhouse experiment when N was homogeneously supplied between the two adjacent pots. Bars represent ±1 standard errors. Points on the X-axis represent the middle age of each age class. Statistical results of the effects of N supply on the relationships between root N concentration and root age are reported in Table S1 available as Supplementary Data at Tree Physiology Online.