Nitrogen mineralization in surface and subsurface layers at forest ecosystems having different soil types

Nakayama, Masataka  ; Abe, Yukiko; Atarashi-Andoh, Mariko  ; Koarashi, Jun   

Plants take up nitrogen mainly from surface soil, while under the nutrient competition, they utilize nitrogen from subsurface soil layers. However, nitrogen dynamics in the subsoil layer is unclear. Here, we investigated the soil profiles (0-60 cm depth) of net nitrogen mineralization and nitrification rates at four Japanese broad-leave forest having two different soil types (volcanic ash and non-volcanic ash soil). The results showed that net nitrogen mineralization decreased with increase of soil depth in the sites of volcanic ash soil, but the trend was not observed in the sites of non-volcanic ash soil. When the rates represented per unit soil volume, the vertical differences in nitrogen mineralization were non-significant for these two soil types. Similar to the factors regulating the spatial variations of nitrogen dynamics, the vertical trends were regulated by the soil total carbon and nitrogen contents and microbial biomass. These results suggested that the quantities of soil organic material and microbes regulated both of the horizontal and vertical differences in the nitrogen dynamics, and that the subsurface soil, as well as surface soil, was quantitatively important nitrogen source for plants.