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Communication Dans Un Congrès Année : 2022

Forest Ecosystem Fertility in a changing world: Novel concepts, tools and approaches to understand the role of the biogeochemical cycles in tree nutrition

Karna Hansson
  • Fonction : Auteur
Jérémie Bel
  • Fonction : Auteur
  • PersonId : 1003858
Jean-Paul Laclau
Laurent Augusto
Jacques Ranger
  • Fonction : Auteur
  • PersonId : 1195809

Résumé

Many forest ecosystems are developed on acidic and nutrient poor soils (particularly in Ca, Mg and K). For Ca, Mg and K, the plant-available pools are assumed to be stored in the soil as exchangeable cations adsorbed on the cationic exchange complex. Because anthropogenic inputs (e.g. fertilization or liming) are not common practices in forestry, on the long term, the plant-available pools in the soil are mainly supplied by the nutrient cation inputs from atmospheric deposition and the weathering of minerals in the soil, and vary as a function of the ecosystem output fluxes: harvested biomass exportation and nutrient leaching in the soil below the rooting zone. Despite this apparent simplicity, it is still unclear how trees cope and how forest productivity is sustained with such low available nutrient resources in the soil. This growing concern is becoming of paramount importance in the context of global and climate change to help give forest managers and policy makers the most accurate picture of the potential of forest ecosystems and associated threats. In this presentation, we will discuss the emerging concepts and the novel approaches in the field of tree nutrition research. The first objective of this presentation is to show, through the study of a compiled dataset of 49 forest ecosystems, the limits of the common definition of soil chemical fertility inherited from agronomy (pool of plant available nutrients in the soil at a given time compared to the nutritional requirement of the tree species) when applied to forest ecosystem contexts. This analysis led to a conceptual framework for a new definition of chemical fertility for forest ecosystems by showing the necessity to include biogeochemical cycling and recycling fluxes in the definition and soil chemical fertility diagnosis methods. We show that the chemical fertility is not only supported by the soil in forest ecosystem but by the sum of all the ecosystem’s compartments and fluxes between these pools. The second objective is to present the recent groundbreaking results in the understanding of plant-available pools and the biological cycling of Mg, Ca and K obtained and from the development of stable isotope tracing techniques. Firstly, the development of stable isotope dilution techniques has enabled to demonstrate that nutrient cation pools stored in secondary non-crystalline minerals contribute directly to geochemical equilibrium reactions in the soil. This suggests that limiting the definition of plant-available pools are much larger than the exchangeable pools. These findings have led us to propose a new conceptual model of nutrient plant-availability. Secondly, the results from an in situ ecosystem-scale multi-isotopic tracing experiment in 30-yr old beech plot with very low resources of Mg and Ca show that nutrient cation inputs to the forest soil are maintained in the soil-plant system through a very slow but very conservative biological cycle. This unique experiment also showed that a significant fraction of nutrient cations stored in aboveground biomass are not immobilized but slowly circulating, suggesting that the tree internal pool of Ca and Mg may be more active than previously thought and that this pool may act as a buffer when nutrient availability is in shortage.
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Dates et versions

hal-04195784 , version 1 (04-09-2023)

Identifiants

  • HAL Id : hal-04195784 , version 1

Citer

Gregory van Der Heijden, Karna Hansson, Jérémie Bel, Jean-Paul Laclau, Laurent Augusto, et al.. Forest Ecosystem Fertility in a changing world: Novel concepts, tools and approaches to understand the role of the biogeochemical cycles in tree nutrition. Eurosoil 2021, Aug 2022, Geneva, Switzerland. ⟨hal-04195784⟩

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