Figure 1

Season × Environment interaction effect on soil (a) NO3 and (b) NH4 supply rate and Season effect on soil (c) P, (d) K, (e) Ca and (f) Mg supply rate in hybrid poplar plantations. P-value of Season × Environment interaction effects are the following (according to MANOVA): NO3 (p = 0.05) and NH4 (p = 0.01). P-value of the Season effect are the following (according to MANOVA): NO3 (p < 0.0001), NH4 (p = 0.0005), P (p = 0.02), K (p = 0.004), Ca (p = 0.03), Mg (p = 0.03). Vertical bars are standard error of the mean.