Nitrogen pools and C:N ratios in well-drained Nordic forest soils related to climate and soil texture

Relationships between soil nitrogen (N) pools, climate, and soil-texture class in well-drained Nordic forest soils may be used for upscaling of regional N budgets. Total soil N pools and C:N ratios were studied in forest soils in Fennoscandia and Denmark (55-70°N, 5-27°E) in boreal pine and spruce forest, boreal mixed forest, and nemoral forest types (beech, oak, mixed). Total N pools in 198 forest soil profiles were calculated from horizon thickness, bulk density, stone content and nitrogen concentration and related to climate and soil texture through multiple linear regressions. The top 100 cm of the mineral soil and the organic layer were included. C:N ratios were calculated from C and N concentrations in 10-cm depth sections. Total soil N pools ranged from 0.05 to 1.65 kg N m -2 and were positively correlated with mean annual temperature (MAT) and mean annual precipitation (MAP). The range of mean annual temperatures was -2 °C to 8.4 °C, and the range of mean annual precipitations was 282 to 2270 mm y -1 . Soil N pools were highly variable and related to climate and soil texture class. The total soil N pools in coarse textured soils changed more with changing MAT and MAP than those in medium textured soils due to lower N pools in coarse soils in the northern part of the study area. C:N ratios were negatively correlated with temperature and precipitation in the uppermost mineral soil layers and the organic layer. C:N ratios of soil organic matter in the organic layer or top mineral soil are indicators of litter quality and degree of humification, but also reflect ecosystem N status in high N deposition areas.