Experiments using 15 N-labeled urea were conducted for three years to assess the effect of N-deposition on soil C and N dynamics under oak (Qa) and pine (Pk) forest stands in natural field conditions. Throughout the experiment, an increase in total C, mineral N, and total N due to N deposition was greater in coniferous forest soils than in deciduous forest soils, while decreasing the pH of both soils as a result of nitrification. Natural 13 C abundance of soil samples was interpreted to reveal the physical mixing of new C substrates from leaf-litter with old C substrates. The δ 13 C of the upper soil layers became more negative, with greater decreases in the Pk soil. However, with time, the lowering of δ 13 C was better maintained in the Pk soil than in the Qa soil, indicating greater incorporation of new C substrates from leaf-litter decomposition into old SOC pools in the Pk soil compared to the Qa soil. We revealed that an increase in total C and N contents due to N deposition was greater under coniferous forest stands than under deciduous forest stands as a result of greater mixing of new C substrates into the soil profile in this temperate forest.
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