*3.3. P Concentration*

Both elevation and time (season) significantly affected the tissue P concentrations, and the elevation × time interaction was significant for P concentrations in aboveground tissues (leaves, shoots, and stem sapwood) (Table 2). Leaf and shoot P concentrations were higher in July than in September, whereas stem and root P concentrations were higher in September than in July (Figure 3a–h). Tissue P concentrations were higher in trees at higher elevations in both July and September, except for P in leaves and shoots in July (Figure 3a–h).

**Figure 3.** Seasonal tissues concentration (Mean ± 1SD; % of dry matter) changes in total phosphorus (P) of *Betula ermanii* trees along elevational gradients in Changbai Mountain (*n* = 5 for each elevational site and tissue type). Different letters display significant differences at the 0.05 level among elevations as determined by Tukey's HSD test.
