09 Sep 2022
09 Sep 2022
Status: this preprint is open for discussion.

Potassium-limitation of forest productivity, part 1: A mechanistic model simulating the effects of potassium availability on canopy carbon and water fluxes in tropical eucalypt stands

Ivan Cornut1,2,5, Nicolas Delpierre1,3, Jean-Paul Laclau2,5, Joannès Guillemot2,4,5, Yann Nouvellon2,6, Otavio Campoe6, Jose Luiz Stape7, Vitoria Fernanda Santos8, and Guerric le Maire2,5 Ivan Cornut et al.
  • 1Université Paris-Saclay, CNRS, AgroParisTech, Ecologie Systématique et Evolution, 91405, Orsay, France
  • 2CIRAD, UMR Eco&Sols, F-34398 Montpellier, France
  • 3Institut Universitaire de France (IUF)
  • 4Department of Forest Sciences ESALQ, University of São Paulo, Piracicaba, São Paulo, Brazil
  • 5Eco&Sols, Univ. Montpellier, CIRAD, INRAe, Institut Agro, IRD, Montpellier, France
  • 6Universidade Federal de Lavras, Departmento de Ciências Florestais, Lavras, MG, Brazil
  • 7Department of Forest Science, São Paulo State University, 18610-034 Botucatu, SP, Brazil
  • 8Suzano Papel e Celulose, Brazil

Abstract. The extent of the potassium (K) limitation of forest productivity is probably more widespread than previously thought, and K-limitation could influence the response of forests to future global changes. To understand the effects of K-limitation on forest primary production, we have developed the first ecophysiological model simulating the K cycle and its interactions with the carbon (C) and water cycles. We focused on the limitation of the gross primary productivity (GPP) by K availability in tropical eucalypt plantations in Brazil. We used results from large-scale fertilisation experiments as well as C flux measurements in two tropical eucalypt plantations to parameterize the model. The model was parameterized for fertilised conditions and then used to test for the effects of contrasting additions of K fertiliser. Simulations showed that K-deficiency limits GPP by more than 50 % during a 6-year rotation, a value in agreement with the literature. The negative effects of K-deficiency on canopy transpiration and water use efficiency were also reported and discussed. Through a sensitivity analysis, we used the model to identify the most critical processes to consider when studying K-limitation of GPP. The external inputs of K to the stands, such as the atmospheric deposition and weathering fluxes, and the regulation of the internal fluxes of K within the ecosystem were critical for the response of the system to K deficiency. Litter decomposition processes were of lower importance. The new forest K-cycle model developed in the present study includes multiple K processes interacting with the carbon and water cycles, and strong feedbacks on GPP through forest growth were outlined.

Ivan Cornut et al.

Status: open (until 21 Oct 2022)

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Ivan Cornut et al.


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Short summary
Potassium is an essential element for living organisms. Trees are dependent upon this element for certain of their functions that allow them to build their trunk using carbon dioxide. Using data from experiments in eucalypt plantations in Brazil and a simplified computer model of the plantations we were able to investigate the effect the lack of potassium can have on the production of wood. Understanding nutrient cycles is useful to understand the response of forests to environmental change.