Effect of water content on the rate of nitrogen mineralization and immobilization in the Ao-layer of forest soils
1998
Toda, H. (Tokyo Univ. of Agriculture and Technology, Fuchu (Japan). Faculty of Agriculture) | Sugisaki, H. | Haibara, K.
The effect of water content on the rate of nitrogen mineralization and immobilization in the A0-layer (F2 and F3 class) of forest soil was studied by sampling from three plots: a plot of cedar (Cryptomeria japonica D. Don) on a lower slope, and a plot of cypress (Chamaecyparis obtusa Endl) on an upper slope and a deciduous broad-leaved plot on an upper slope. The samples were incubated in vitro for 44 days at 25 degree C with water contents of 90, 180, and 270 %. The rate of nitrogen mineralization and immobilization 8 days after incubation was measured using the 15N-isotope dilution method. In the F3 class, low water content (90 %) reduced the rate of net nitrogen mineralization. Nitrification was observed only in the cedar plot on the lower slope, and it increased at higher water contents. Nitrification was not observed in the cypress or broad-leaved plots although the water contents was high. Both the rate of nitrogen mineralization (Vm) and immobilization (Vl) decreased at 90 % water content treatment except for F2 class of the cypress plot. The effect of water content on the Vl/Vm ratio was greatest in the cypress and broad-leaved plots. It was concluded that this was because the microbial flora adjusting to dryness was formed on the dried upper slopes
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