Fig. 7. Relationships between leaf nitrogen (N) concentration and (a–f) various single-waveband canopy reflectance ratios across different N treatments and sampling dates. Best-fit regression lines are represented by solid lines, with the exception of R₇₅₅/R₇₀₀ for which a dashed line is used to represent the regression function when leaf N values > 40 g kg^-1 are excluded (df = 17, r² = 0.82**). **Significant at P < 0.01; otherwise, not significant (ns).