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Communication Dans Un Congrès Année : 2018

Quantification of the sources of calcium magnesium and potassium in forest soils and their plant-availability by a multi-isotopic tracing and dilution approach

Jérémie Bel
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Laurent Saint‐andré

Résumé

Forest ecosystems are generally developed on acid and nutrient-poor soils. Plant-available pools of Mg, Ca, and K are assumed to be stored in the soil as exchangeable cations adsorbed on the cation exchange complex (exchangeable pools) are traditionally measured by cation exchange soil extractions. In the long term, these plant-available pools in the soil vary as a function of Mg, Ca and K inputs to the ecosystem (mineral weathering in the soil, atmospheric and possible anthropogenic inputs) and the outputs (biomass storage/harvest, nutrient leaching). However, this model has been questioned by many studies which suggest that nutrient sources in forest ecosystems that currently are not taken into account accurately or at all may contribute directly to plant availability and biogeochemical processes. Between soil minerals and exchangeable cations exists a gradient of Mg, Ca, and K storage forms that have not been fully characterized and may play an important role in plant nutrition and biogeochemical cycles. We hypothesize that sources of Mg, Ca, and K in the soil other than the conventionally measured exchangeable pools are plant-available on very short time scales (<1 day). The pools of Mg, Ca, and K in the soil that contribute directly to equilibrium processes between the liquid and solid phases of the soil (isotopically exchangeable pools) were quantified using a novel stable multi-isotopic (26Mg, 44Ca, and 41K) tracing and dilution techniques. 25 forest sites were selected within several networks of monitoring or experimental plots in order to cover a wide range of soil, climate and silvicultural contexts. The isotopically exchangeable pools were measured in different soil layers of a composite profile at each site. Different soil extractions (ammonium acetate and nitric acid) were performed to measure the distribution of isotopic tracers in the solid phases of the soil. For 67%, 70% and 49% of the analyzed samples, the respective isotopically exchangeable pools of K, Mg and Ca were equal or greater than the exchangeable pool (conventional method). In addition, isotopic tracers of Ca, K and Mg were recovered in soil phases (non-crystalline mineral phases) that are not commonly considered to contribute to source/sink equilibrium reactions. The isotopic dilution method is a relevant tool to quantify the plant-available pools of Mg, Ca, and K on short time scales (source and sink pools) and is a very promising approach to characterize and quantify the processes responsible for the depletion and/or replenishment of these pools over longer time scales.

Domaines

Science des sols
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Dates et versions

hal-04195792 , version 1 (04-09-2023)

Identifiants

  • HAL Id : hal-04195792 , version 1

Citer

Jérémie Bel, Arnaud Legout, Laurent Saint‐andré, Gregory van Der Heijden. Quantification of the sources of calcium magnesium and potassium in forest soils and their plant-availability by a multi-isotopic tracing and dilution approach. Functional Ecology Conference 2018, Dec 2018, Nancy, France. ⟨hal-04195792⟩

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