Functional specialization of Eucalyptus fine roots: contrasting potential uptake rates for nitrogen, potassium and calcium tracers at varying soil depths

Authors

  • Eduardo Vinícius da Silva,

    1. USP, ESALQ, 11 Av. Pádua Dias, Piracicaba, SP, CEP 13418-900, Brazil
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  • Jean-Pierre Bouillet,

    Corresponding author
    1. USP, ESALQ, 11 Av. Pádua Dias, Piracicaba, SP, CEP 13418-900, Brazil
    2. CIRAD, UMR Eco&Sols – Ecologie Fonctionnelle & Biogéochimie des Sols & Agroécosystèmes (SupAgro-CIRAD-INRA-IRD), 2 Place Viala, F34060 Montpellier, France
      Corresponding author. E-mail: jpbouillet@cirad.fr
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  • José Leonardo de Moraes Gonçalves,

    1. USP, ESALQ, 11 Av. Pádua Dias, Piracicaba, SP, CEP 13418-900, Brazil
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  • Cassio Hamilton Abreu Junior,

    1. USP, CENA, 303 Av. Centenário, Piracicaba, SP, CEP 13416-000, Brazil
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  • Paulo Cesar Ocheuze Trivelin,

    1. USP, CENA, 303 Av. Centenário, Piracicaba, SP, CEP 13416-000, Brazil
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  • Philippe Hinsinger,

    1. INRA, UMR Eco&Sols – Ecologie Fonctionnelle & Biogéochimie des Sols & Agroécosystèmes (SupAgro-CIRAD-INRA-IRD), 2 Place Viala, F34060 Montpellier, France
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  • Christophe Jourdan,

    1. CIRAD, UMR Eco&Sols – Ecologie Fonctionnelle & Biogéochimie des Sols & Agroécosystèmes (SupAgro-CIRAD-INRA-IRD), 2 Place Viala, F34060 Montpellier, France
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  • Yann Nouvellon,

    1. CIRAD, UMR Eco&Sols – Ecologie Fonctionnelle & Biogéochimie des Sols & Agroécosystèmes (SupAgro-CIRAD-INRA-IRD), 2 Place Viala, F34060 Montpellier, France
    2. USP, Departmento de Ciências Atmosféricas, Rua do Matão, 1226, 05508-090, São Paulo, Brazil Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, North Carolina, USA
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  • José Luiz Stape,

    1. USP, Departmento de Ciências Atmosféricas, Rua do Matão, 1226, 05508-090, São Paulo, Brazil Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, North Carolina, USA
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  • Jean-Paul Laclau

    1. CIRAD, UMR Eco&Sols – Ecologie Fonctionnelle & Biogéochimie des Sols & Agroécosystèmes (SupAgro-CIRAD-INRA-IRD), 2 Place Viala, F34060 Montpellier, France
    2. USP Departamento de Ecologia, Rua do Matão, 321, 05508-900, São Paulo, Brazil
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Corresponding author. E-mail: jpbouillet@cirad.fr

Summary

1. Little is known about the role of deep roots in the nutrition of forest trees and their ability to provide a safety-net service taking up nutrients leached from the topsoil.

2. To address this issue, we studied the potential uptake of N, K and Ca by Eucalyptus grandis trees (6 years of age – 25 m mean height), in Brazil, as a function of soil depth, texture and water content. We injected inline image-15N, Rb+ (analogue of K+) and Sr2+ (analogue of Ca2+) tracers simultaneously in a solution through plastic tubes at 10, 50, 150 and 300 cm in depth in a sandy and a clayey Ferralsol soil. A complete randomized design was set up with three replicates of paired trees per injection depth and soil type. Recently expanded leaves were sampled at various times after tracer injection in the summer, and the experiment was repeated in the winter. Soil water contents were continuously monitored at the different depths in the two soils.

3. Determination of foliar Rb and Sr concentrations and 15N atom % made it possible to estimate the relative uptake potential (RUP) of tracer injections from the four soil depths and the specific RUP (SRUP), defined as RUP, per unit of fine root length density in the corresponding soil layer.

4. The highest tracer uptake rates were found in the topsoil, but contrasting RUP distributions were observed for the three tracers. Whilst the RUP was higher for inline image-15N than for Rb+ and Sr2+ in the upper 50 cm of soil, the highest SRUP values for Sr2+ and Rb+ were found at a depth of 300 cm in the sandy soil, as well as in the clayey soil when gravitational solutions reached that depth.

5. Our results suggest that the fine roots of E. grandis trees exhibit contrasting potential uptake rates with depth depending on the nutrient. This functional specialization of roots might contribute to the high growth rates of E. grandis trees, efficiently providing the large amounts of nutrients required throughout the development of these fast-growing plantations.

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