It is still unclear how soil pH differentiates soil nitrogen dynamics under tropical forests. To evaluate the effect of soil pH, we compared the soil N dynamics of tropical seasonal forests under different soil pH conditions in Cameroon.

This study was carried out in forested sites in eastern (A) (A horizon pH = 4.2, Oxisol) and southern (E) (A horizon pH = 3.5, Ultisol) Cameroon. Soil solutions by tension-free lysimeters at 30 cm depth and litter leachate (beneath O horizon), and throughfall were monthly collected.

Nitrate fluxes in the O horizon at site A (118.9 kg-N ha^-1 yr^-1) were 6 times as high as those in throughfall (19.2 kg-N ha^-1 yr^-1), while no difference was detected at site E (11.8-12.0 kg-N ha^-1 yr^-1). Conversely, nitrate fluxes in soil solution at 30 cm from both sites were substantially low (11.5 kg-N ha^-1 yr^-1 at site A, 4.9 kg-N ha^-1 yr^-1 at site E) compared with each O horizon. Therefore, it indicates that N is absorbed by plants at both the O horizon and mineral soil (0–30 cm) at forested sites with moderately acidic soil (A), whereas N is mostly absorbed within the O horizon with a thick root mat but not at mineral soil in a highly acidic soil (E).