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Nitrogen limitation in eucalypt roots: a cascading influence on the mobilization of soil organic matter

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Abstract

Emerging scientific evidence has shown that root exudates may trigger the mobilization of soil organic matter (SOM), particularly under nutrient limitation. However, the role of changes in root morphology, metabolism, exudation, and their impact on rhizospheric properties and SOM remain poorly known. To address this issue, we conducted a rhizobox experiment for 50 days in which pre-grown eucalypt plants (120 days-old) were supplied with nutrient solutions providing either limited (0.0 mg L− 1) or normal N supply (196.0 mg L− 1). After 48 days, we used a 13CO2 pulse labeling to track the impact of N limitation on C translocation to roots and soil respiration. After the 50th day, we assessed root morphology and metabolism, rhizospheric pH, mineral crystallinity, C and N contents, and the molecular composition of SOM. Under N limitation, eucalypt plants showed reduced photosynthesis, increased their root-to-shoot ratio and root branching, with organic acids prevailing among root metabolites. Overall, N-limited eucalypt plants led to a cascading of changes in the rhizosphere: increased concentrations of recently fixed 13C-CO2, citrate, and N-bearing compounds, whereas soil pH and Fe-bound SOM decreased. These results were not followed by significant changes in microbial biomass, neither fungi: bacteria nor Gram-positive: Gram-negative ratios. Our results show that under N limitation, eucalypt roots exhibited a cascade of morpho-physiological adjustments that ultimately increased the mobilization of some SOM pools. Therefore, the combined impacts of those root morpho-physiological traits on the mobilization of SOM may reduce the overall soil C sink of eucalypt forests under N limitation.

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Acknowledgements

We thank João Milagres and Humberto Rosado for their support during lab analyses. This research used resources of the Brazilian Synchrotron Light Laboratory (LNLS), an open national facility operated by the Brazilian Centre for Research in Energy and Materials (CNPEM) for the Brazilian Ministry for Science, Technology, Innovations and Communications (MCTIC). The XPD beamline staff is acknowledged for the assistance during the experiments.

Funding

We thank the funding provided by the Brazilian Government, grant No. 406840 − 143060, as part of the National Research Program NRP68 “Soil as a Resource”. Both I.R.S. and L.V. received funds from the Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico (CNPq) and I.F.S received funding from the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) as part of the Estágio Pós-Doutoral do Programa Nacional de Pós-Doutorado/Capes (PNPD/CAPES), grant number 88887.356500/2019-00. The work was also funded by the Sociedade de Pesquisas Florestais (SIF) as part of the research unit “NUTREE”.

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Conceptualization: L.C.C.H; Methods: L.C.C.H, R.T.Á, L.F.A, G.S; Formal analysis and investigation: L.C.C.H, I.F.S; Writing - original draft preparation: L.C.C.H Writing - review and editing: L.C.C.H, I.F.S; Funding acquisition: I.R.S, L.V Resources: I.R.S; Supervision: I.R.S. All authors read and approved the paper.

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Correspondence to Ivan Francisco Souza.

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Hurtarte, L.C.C., Souza, I.F., Ávila, R.T. et al. Nitrogen limitation in eucalypt roots: a cascading influence on the mobilization of soil organic matter. Biol Fertil Soils 60, 713–726 (2024). https://doi.org/10.1007/s00374-024-01832-x

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  • DOI: https://doi.org/10.1007/s00374-024-01832-x

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