Preprints
https://doi.org/10.5194/bg-2021-188
https://doi.org/10.5194/bg-2021-188

  04 Aug 2021

04 Aug 2021

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

Leaching of inorganic and organic phosphorus and nitrogen in contrasting beech forest soils – seasonal patterns and effects of fertilization

Jasmin Fetzer1,2, Emmanuel Frossard2, Klaus Kaiser3, and Frank Hagedorn1 Jasmin Fetzer et al.
  • 1Forest Soils and Biogeochemistry, Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmensdorf, Switzerland
  • 2Department of Environmental Systems Science, ETH Zurich, Zürich, Switzerland
  • 3Soil Science and Soil Protection, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany

Abstract. Leaching is one major pathway of phosphorus (P) and nitrogen (N) losses from forest ecosystems. Using a full factorial N×P fertilization and irrigation experiment, we investigated the leaching of dissolved organic and inorganic P (DOP and DIP) and N (DON and DIN) from organic layers (litter, Oe/Oa horizons) and mineral A horizons at two European beech sites of contrasting P status. Leachates showed highest DIP and DIN concentrations in summer and lowest in winter, while dissolved organic forms remained rather constant throughout seasons. During the dry and hot summer 2018, DOC : DOP and DOC : DON ratios in leachates were particularly narrow, suggesting a release of microbial P due to cell lysis by drying and rewetting. This effect was stronger at the low-P site. The estimated annual mean fluxes from the Oe/Oa horizons in the non-fertilized treatment were 60 and 30 mg m−2 yr−1 for total dissolved P and 730 and 650 mg m−2 yr−1 for total dissolved N at the high-P and the low-P site, respectively. Fluxes of P were highest in the organic layers and decreased towards the A horizon, likely due to sorption by minerals. Fertilization effects were additive at the high-P, but antagonistic at the low-P site: At the high-P site, fertilization with +N, +P, and +N+P increased total P fluxes from the Oe/Oa horizon by +33, +51, and +75 %, while the respective increases were +198, +156, and +10 % at the low-P site. The positive N-effect on DIP leaching possibly results from a removed N limitation of phosphatase activity at the low-P site. Fluxes of DOP remained unaffected by fertilization. Fluxes of DIN and DON from the Oe/Oa horizons increased upon +N and +N+P, but not upon +P fertilization. In conclusion, the estimated P fluxes from the A horizons were comparable in magnitude to reported atmospheric P inputs, suggesting that these systems do not deplete in P due to leaching. However, a particularly high sensitivity of DIP leaching to hotter and drier conditions suggests accelerated P losses under the expected more extreme future climate conditions. Increases of P leaching due to fertilization and drying-rewetting were higher in the low-P system, implying that the low-P system is more susceptible to environmental future changes.

Jasmin Fetzer et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-188', Anonymous Referee #1, 13 Sep 2021
  • RC2: 'Comment on bg-2021-188', Lukas Kohl, 17 Oct 2021

Jasmin Fetzer et al.

Jasmin Fetzer et al.

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Short summary
As leaching is a major pathway of nitrogen and phosphorus loss in forest soils, we investigated several potential drivers in two contrasting beech forests. The composition of leachates, obtained by zero-tension lysimeters, varied with seasons, and climatic extremes influenced the magnitude of leaching. Effects of nitrogen and phosphorus fertilization varied with soil nutrient status and sorption properties, and leaching from the low-nutrient soil was more sensitive to environmental factors.
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