- Department of Soil and Environment, Swedish University of Agricultural Sciences
Spatial patterns of nitrogen isotope ratios in forest soils are related to latitude and soil phosphorus concentration
Spohn, Marie; Stendahl, Johan
The aim of this study was to identify the parameters that affect the nitrogen (N) isotope ratio (& delta;N-15) in soils of temperate and boreal forests. We measured the & delta;N-15 in 30 soil profiles of temperate and boreal forests in Sweden and analyzed the relationships between & delta;N-15 in the soils and soil chemical properties as well as site characteristics. In addition, we conducted a meta-analyses of & delta;N-15 in the organic layer of European forests. We identified two types of & delta;N-15 patterns; in type D soils, the & delta;N-15 in the mineral soil decreases with depth, whereas in type C soil, the & delta;N-15 in the soil profile is almost constant. Type D soils had a significantly higher & delta;N-15 in the organic layer and upper mineral soil than type C soils, which is likely due to N isotope fractionation by ectomycorrhizal fungi in the topsoil. Type D soils were found in boreal forests, but not in temperate forests. They had a significantly lower atmospheric N deposition rate than type C soils, by a factor of 2.3, and a significantly higher phosphorus (P) concentration of the organic layer than type C soils, by a factor of 1.5. We also found that the & delta;N-15 was negatively correlated with the N:P ratio of the organic layer (R-2 = 0.21, p < 0.001). Across Europe, the & delta;N-15 of the organic layer was positively correlated with latitude (R-2 = 0.58, p < 0.001), and negatively with mean annual temperature (R-2 = 0.52, p < 0.001) and atmospheric N deposition (R-2 = 0.42, p < 0.001). In conclusion, our results show that the & delta;N-15 of the organic layer and microbial N (re-)cycling in forest soils is positively related with latitude and the P concentration of the organic layer.
Nitrogen isotopes; Temperate forest; Boreal forest; Latitude; Phosphorus concentration; Atmospheric nitrogen deposition
2023, Volume: 165, number: 1, pages: 43 - 56
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