Preprints
https://doi.org/10.5194/bg-2021-346
https://doi.org/10.5194/bg-2021-346

  22 Dec 2021

22 Dec 2021

Review status: this preprint is currently under review for the journal BG.

Carbon, nitrogen, and phosphorus stoichiometry of organic matter in Swedish forest soils and its relationship with climate, tree species, and soil texture

Marie Spohn and Johan Stendahl Marie Spohn and Johan Stendahl
  • Department of Soil and Environment, Swedish University of Agricultural Sciences (SLU), Lennart Hjelms väg 9, P.O. Box 7014, 75007 Uppsala, Sweden

Abstract. While the carbon (C) content of temperate and boreal forest soils is relatively well studied, much less is known about the ratios of C, nitrogen (N), and phosphorus (P) of the soil organic matter, and the abiotic and biotic factors that shape them. Therefore, the aim of this study was to explore carbon, nitrogen, and organic phosphorus (OP) contents and element ratios in temperate and boreal forest soils and their relationships with climate, dominant tree species, and soil texture. For this purpose, we studied 309 forest soils with a stand age >60 years located all over Sweden between 56° N and 68° N. The soils are a representative subsample of Swedish forest soils with a stand age >60 years that were sampled for the Swedish Forest Soil Inventory. We found that the N stock of the organic layer increased by a factor of 7.5 from −2 °C to 7.5 °C mean annual temperature (MAT), it increased almost twice as much as the organic layer stock along the MAT gradient. The increase in the N stock went along with an increase in the N : P ratio of the organic layer by a factor of 2.1 from −2 °C to 7.5 °C MAT (R2 = 0.36, p < 0.001). Forests dominated by pine had higher C : N ratios in the litter layer and mineral soil down to a depth of 65 cm than forests dominated by other tree species. Further, also the C : P ratio was increased in the pine-dominated forests compared to forests dominated by other tree species in the organic layer, but the C : OP ratio in the mineral soil was not elevated in pine forests. C, N and OP contents in the mineral soil were higher in fine-textured soils than in coarse-textured soils by a factor of 2.3, 3.5, and 4.6, respectively. Thus, the effect of texture was stronger on OP than on N and C, likely because OP adsorbs very rigidly to mineral surfaces. Further, we found, that the P and K concentrations of the organic layer were inversely related with the organic layer stock. The C and N concentrations of the mineral soil were best predicted by the combination of MAT, texture, and tree species, whereas the OP concentration was best predicted by the combination of MAT, texture and the P concentration of the parent material in the mineral soil. In the organic layer, the P concentration was best predicted by the organic layer stock. Taken together, the results show that the N : P ratio of the organic layer was most strongly related to MAT. Further, the C : N ratio was most strongly related to dominant tree species, even in the mineral subsoil. In contrast, the C : P ratio was only affected by dominant tree species in the organic layer, but the C : OP ratio in the mineral soil was hardly affected by tree species due to the strong effect of soil texture on the OP concentration.

Marie Spohn and Johan Stendahl

Status: open (until 02 Feb 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Referee comment on “Carbon, nitrogen and phosphorus stoichiometry of organic matter in Swedish forest soils and its relationship with climate, tree species, and soil texture”', Anonymous Referee #1, 31 Dec 2021 reply
  • RC2: 'Comment on bg-2021-346', Anonymous Referee #2, 17 Jan 2022 reply
  • RC3: 'Comment on bg-2021-346', Anonymous Referee #3, 21 Jan 2022 reply

Marie Spohn and Johan Stendahl

Marie Spohn and Johan Stendahl

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Short summary
Temperate and boreal forests store large amounts of soil organic matter (SOM). We explored the ratios of carbon (C), nitrogen (N), and phosphorus (P) of SOM in Swedish forest soils Sweden. The N : P ratio of the organic layer was most strongly related to the mean annual temperature, the C : N ratios of the organic layer and mineral soil were most strongly related to tree species, and the C-to-organic P (C : OP) ratio of the mineral soil was strongly affected by soil texture.
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