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| Chang, S-C; Matzner, E: Soil nitrogen turnover in proximal and distal stem areas of European beech trees, Plant and Soil, 218, 117-125 (2000) | |
Abstract:
In European beech (Fagus sylvatica L.) forests, a large proportion of the water and ion input to the soil results from
stemflow which creates a soil microsite of high element fluxes proximal to the tree trunk. The soil proximal to the
stem is considered to have different rates of nitrogen turnover which might influence the estimation of N-turnover
rates at the stand scale. In a previous study we reported high nitrate fluxes with seepage proximal to the stems in a
forest dominated by European beech in Steigerwald, Germany. Here, we investigated the soil nitrogen turnover in
the top 15 cm soil in proximal (defined as 1 m2 around beech stems) and distal stem areas. Laboratory incubations
and in situ sequential coring incubations were used to determine the net rates of ammonification, nitrification,
and root uptake of mineral nitrogen. In the laboratory incubations higher rates of net nitrogen mineralization and
nitrification were found in the forest floor proximal to the stem as compared to distal stem areas. No stem related
differences were observed in case of mineral soil samples. In contrast, the in situ incubations revealed higher rates
of nitrification in the mineral soil in proximal stem areas, while net nitrogen mineralization was equal in proximal
and distal areas. In the in situ incubations the average ratio of nitrification/ammonificationwas 0.85 in proximal and
0.34 in distal stem areas. The net nitrogen mineralization was 4.4 g N m2 90 day1 in both areas. Mineralized
nitrogen was almost completely taken up by tree roots with ammonium as the dominant nitrogen species. The
average ratio of nitrate/ammonium uptake was 0.69 in proximal and 0.20 in distal areas. The higher water content
of the soil in proximal stem areas is considered to be the major reason for the increased rates of nitrification.
Different nitrogen turnover rates in proximal stem areas had no influence on the nitrogen turnover rates in soil at
the stand scale. Consequently, the observed high nitrate fluxes with seepage proximal to stems are attributed to the
high nitrogen input by stemflow rather than to soil nitrogen turnover. |
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