Nitrate production in nitrogen-saturated acid forest soils: Vertical distribution and characteristics

Abstract

In order to study the vertical distribution, nature and pH-dependence of nitrate production in nitrogen-saturated acid forest soils, an incubation experiment was carried out using soil cores from five Dutch forests. Soil cores were left intact during incubation and divided into L, F, H horizons and top 5 cm of the mineral soil before analysis. One of the five forest soils revealed no significant NO 3 production during incubation, while in the other four sites different patterns with respect to vertical distribution of NO 3 production were found. The two coniferous sites snowed a dominance of NO 3 production in the ectorganic horizon (L + F + H), while in the two deciduous forests the production of NO 3 in the ectorganic horizon and in the top 5 cm of the mineral soil contributed about equally to total nitrification. At one of the deciduous sites, nitrification in the 5 cm top layer of the mineral soil was higher than the separate NO 3 productions in the L, F and H layer. Experiments with acetylene as a selective inhibitor indicated that the measured NO 3 production in the F layer of all four nitrifying forest sites was mainly carried out by chemolithotrophic bacteria. In the dominant nitrifying compartments, nitrification was mainly found to be acid-tolerant, which underlines the importance of this type of nitrification in N-saturated forest soils.