Preprints
https://doi.org/10.5194/soil-2020-94
https://doi.org/10.5194/soil-2020-94

  04 Jan 2021

04 Jan 2021

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

Nutrient limitations regulate soil greenhouse gas fluxes from tropical forests: evidence from an ecosystem-scale nutrient manipulation experiment in Uganda

Joseph Tamale1,5, Roman Hüppi4, Marco Griepentrog3, Laban Frank Turyagyenda5, Matti Barthel4, Sebastian Doetterl3, Peter Fiener1, and Oliver van Straaten2,6 Joseph Tamale et al.
  • 1Institute of Geography, University of Augsburg, Augsburg, 86159, Germany
  • 2Environmental Control Department, Nordwestdeutsche Fortlische Versuchanstalt, Göttingen, 37079, Germany
  • 3Soil Resources, Department of Environmental Systems Science, ETH, Zurich, 8092, Switzerland
  • 4Sustainable Agroecosystems, Department of Environmental Systems Science, ETH, Zurich, 8092, Switzerland
  • 5Ngetta Zonal Agricultural Research and Development Institute (NGEZARDI), P.O.Box 52, Lira, Uganda
  • 6Soil Science of Tropical and Subtropical Ecosystems, Büsgen-Institute, University of Göttingen, Göttingen, 37077, Germany

Abstract. Tropical forests contribute significantly to the emission and uptake of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). However, studies on the soil environmental controls of greenhouse gases (GHGs) from African tropical forest ecosystems are still rare. The aim of this study was to disentangle the regulation effect of soil nutrients on soil GHG fluxes in a tropical forest in northwestern Uganda. Therefore, a large-scale nutrient manipulation experiment (NME) based on 40 m × 40 m plots with different nutrient addition treatments (nitrogen (N), phosphorus (P), N + P, and control) was established. Soil CO2, CH4, and N2O fluxes were measured monthly using permanently installed static chambers for 14 months. Total soil CO2 fluxes were partitioned into autotrophic and heterotrophic components through a root trenching treatment. In addition, soil temperature, soil water content, and mineral N were measured in parallel to GHG fluxes. N addition (N, N + P) resulted in significantly higher N2O fluxes in the transitory phase (0–28 days after fertilization, p < 0.01), because N fertilization likely increased soil N beyond the microbial immobilization and plant nutritional demands leaving the excess to be nitrified or denitrified. Prolonged N fertilization however, did not elicit a significant response in background (measured more than 28 days after fertilization) N2O fluxes. P fertilization marginally and significantly increased transitory (p = 0.052) and background (p = 0.010) CH4 consumption, probably because it enhanced methanotrophic activity. Addition of N and P together (N + P) resulted in larger CO2 fluxes in the transitory phase (p = 0.010), suggesting a possible co-limitation of N and P on soil respiration. Heterotrophic (microbial) CO2 effluxes were significantly higher than the autotrophic (root) CO2 effluxes (p < 0.001) across all treatment plots with microbes contributing about three times more to the total soil CO2 effluxes compared to roots (p < 0.001). However, neither heterotrophic nor autotrophic respiration significantly differed between treatments. The results from this study suggest that the feedback of tropical forests to the global soil GHG budget could be disproportionately altered by changes in N and P availability in these biomes.

Joseph Tamale 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 soil-2020-94', Anonymous Referee #1, 03 Feb 2021
    • AC1: 'Reply on RC1', Joseph Tamale, 08 Apr 2021
  • RC2: 'Comment on soil-2020-94', Anonymous Referee #2, 23 Mar 2021
    • AC2: 'Reply on RC2', Joseph Tamale, 08 Apr 2021

Joseph Tamale et al.

Joseph Tamale et al.

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Short summary
Soil greenhouse gas (GHG) fluxes were measured monthly from nitrogen (N), phosphorous (P), N + P, and control plots of the first nutrient manipulation experiment located in an African pristine tropical forest using static chambers. The results suggest; (1) contrasting soil GHG responses to nutrient addition hence highlight the complexity of the tropical forests, (2) that the feedback of tropical forests to the global soil GHG budget could be altered by changes in N and P availability.