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Encroachment of shrubs into subalpine grasslands in the Pyrenees changes the plant-soil stoichiometry spectrum

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Shrub encroachment has been reported over a large proportion of the subalpine grasslands across Europe and is expected to have an important impact on the biogeochemical cycle of these ecosystems. We investigated the stoichiometric changes in the plant-soil system along the succession (e.g. increase in encroachment from unencroached grassland to mature shrubland) at two contrasting sites in the Pyrenees.


We analyzed the chemical composition (C, N,15N, P, K, Ca, Mg and Fe) in the soil and in the aboveground plant compartments (leaves, leaf-litter and stems) of the main herbaceous species and shrubs at three contrasting stages of the succession: unencroached grassland, young shrubland and mature shrubland.


The plant-soil stoichiometry spectrum differed between the successional stages. Shrub encroachment generally increased the concentration of C and Ca and the C:N ratio and often reduced to concentrations of N, P and K in the leaves and leaf-litter, while several soil nutrient concentrations (N, P, K Ca and Mg) decreased. The stocks of C, N, P, Ca, and Mg in the total aboveground biomass increased with encroachment.


Shrub encroachment favored the dominance of long-lived species with low concentrations of N and P in the plant-soil compartments, high C:nutrient ratios in the aboveground biomass and increase the uptake of N through ericoid or ectomycorrhizal fungi. We highlight the role of shrubs in the sequestration of C and nutrients through the allocation to the aboveground biomass. The changes in plant-soil elemental composition and stocks suggest a slowdown of the biogeochemical cycles in the subalpine mountain areas where shrub encroachment occurred.

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We thank all the people who were involved in the field and laboratory work and Jose V. Roses-Díaz for his comments that helped to improve this manuscript. We thank two anonymous reviewers for their contribution to improve this manuscript. This research was supported by the Spanish Government grant [CGL2016-79835], Catalan Government grant SGR 2017-1005, European Research Council Synergy grant ERC-SyG-2013-610028, IMBALANCE-P, and the Spanish National Parks agency (OAPN) through the ARBALMONT project [634S/2012].

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Correspondence to Ifigenia Urbina.

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Responsible Editor: François Teste.

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Urbina, I., Grau, O., Sardans, J. et al. Encroachment of shrubs into subalpine grasslands in the Pyrenees changes the plant-soil stoichiometry spectrum. Plant Soil 448, 37–53 (2020).

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