Figure 2.

The relationships between fine root production (Mg ha⁻¹ yr⁻¹) and soil phosphorus concentration (mg kg⁻¹). Regression lines were plotted with p < 0.05: boreal forests (r² = 0.029, p = 0.196, n = 59), temperate/subtropical forests (r² = 0.149, p < 0.01, n = 53), lowland tropical forests (r² = 0.117, p = 0.04, n = 34), montane tropical forests (r² = 0.058, p = 0.311, n = 20), temperate grasslands (r² = 0.159, p = 0.036, n = 28), tropical grasslands/savannah (r² = 0.752, p < 0.001, n = 14), tundra (r² = 0.195, p = 0.114, n = 14) and wetlands (r² = 0.553, p = 0.034, n = 8). The curved lines indicate the predicted values from monotonically fitted models using BRT analysis. Owing to the small dataset size, BRT is not performed in tundra, wetlands, grasslands and montane tropical forests.