Abstract
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• In this study we analyzed heterogeneity in nutrient cycling induced by trees in Mediterranean annual grasslands, comparing years of higher and lower than average precipitation and analyzing the effects of two different solar radiation scenarios.
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• Organic matter and consequently upper soil N, K, Ca and Mg were significantly greater in those locations receiving the highest levels of solar radiation, and as expected from many other studies in the literature, there was an increase in all macronutrients (except P) as well as pH below the canopy.
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• Contrary to what was expected, plant nutrient concentrations did not directly reflect those found in the soil, with the exception of K. The studied grassland responded to increased nutrient availability by enhancing growth and changing botanical composition rather than by increasing plant nutrient concentrations. Hence, the total amount of accumulated nutrients in the ecosystem was larger below the tree than outside it, although this is mainly a consequence of plant growth enhancement. The levels of Ca, Mg, and Na in plants decreased during the driest year, and the N content was mostly determined by the composition of the grass.
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• Temporal nutrient variability, particularly within-years, explained most of the variability in plant nutrient concentration, while spatial variability induced by trees was determined to be of secondary importance. These results are significant for ecosystem nutrient modelling.
Résumé
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• Dans cette étude, nous avons analysé l’hétérogénéité du cycle des nutriments induite par les arbres dans les prairies méditerranéennes annuelles, en comparant les années à précipitations supérieures et inférieures à la moyenne et en analysant les effets de deux scénarios de rayonnements solaires différents.
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• La matière organique et par conséquent N, K, Ca et Mg des horizons supérieurs du sol étaient significativement plus élevés dans les stations recevant le plus de rayonnement solaire. Comme prévu à partir de nombreuses autres études dans la littérature, une augmentation de tous les macronutriments (sauf P) et aussi du pH a été observée sous la canopée des arbres.
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• Contrairement à ce qui était prévu, les concentrations de nutriments dans les végétaux n’ont pas reflété directement celles trouvées dans le sol, à l’exception de K. Les prairies étudiées ont répondu à un accroissement de la disponibilité en éléments nutritifs par une augmentation de la croissance et un changement de la composition botanique plutôt que par une augmentation des concentrations de nutriments dans les plantes. Par conséquent, les quantités totales de nutriments accumulées dans l’écosystème étaient plus importantes sous les arbres qu’en plein découvert, bien que cela soit principalement une conséquence de l’amélioration de la croissance des plantes. Les niveaux de Ca, Mg, et Na dans les plantes ont diminué au cours de l’année la plus sèche et la teneur en nutriments azotés était largement déterminée par la composition de l’herbe.
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• La variabilité temporelle intra-annuelle des éléments nutritifs expliquait la plus forte part de la variabilité de la concentration en nutriments des plantes annuelles, tandis que la variabilité spatiale induite par les arbres était d’importance secondaire. Ces résultats sont importants pour la modélisation des éléments nutritifs dans les écosystèmes.
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Gea-Izquierdo, G., Allen-Díaz, B., San Miguel, A. et al. How do trees affect spatio-temporal heterogeneity of nutrient cycling in mediterranean annual grasslands?. Ann. For. Sci. 67, 112 (2010). https://doi.org/10.1051/forest/2009091
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DOI: https://doi.org/10.1051/forest/2009091