Partenaires et organisations internationales
(Anglais)
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A, B, HR, CZ, DK, EE, FIN, F, D, GR, H, IS, IRL, I, LT, NL, N, PL, P, RO, E, S, CH, GB
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Résumé des résultats (Abstract)
(Anglais)
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Forests may mitigate the carbon dioxide (CO2) enrichment of the Earth's atmosphere through an increasing productivity under elevated CO2. As the availability of nutrients will probably not increase proportionally with CO2, nutrient limitation may, in turn, reduce the plant response to elevated CO2. Since the C and nutrient cycles - especially nitrogen (N) - are closely associated, the CO2 effect on nutrients is of key importance for the C sequestration. In this experiment we monitored continuously the nutritional status in the soil under control and CO2-fumigated trees in an undisturbed 120 years old mixed forest (experiment of the University of Basel at Hofstetten, NW Switzerland). Ceramic suction cups were installed at depths of 5 and 15 cm along 3 transects through the experimental area under control and CO2-treated trees: one transect under beech (Fagus sylvatica), one under oak (Quercus robur, Q. petraea) and one under hornbeam (Carpinus betulus). At 10 locations along each transect, soil solutions were collected every 14-28 days and analysed for nutrients. As the CO2 used for fumigation is 13C-depleted, we used the 13C depletion in the inorganic C of the soil solution a measure of the treatment impact at the locations of suction cups. In addition to the temporal dynamics of soil solution N, integrative measurements of nitrate and ammonium were made with mixed anion and cation exchange resin bags remaining 6 months in the soil. Nitrate in the soil solution showed a typical seasonal pattern with higher concentrations during the winter. Over more than 3 years of sampling, these concentrations increased less in those locations with a strong 13C-depletion than where the CO2 impact was low. The N nutrition of adult trees thus appears to become more limiting under elevated atmospheric CO2 concentrations. Because of differences in nitrate concentrations present already at the beginning of the experiment, it is not possible to draw clear conclusions from this experimental effect, even if it is statistically significant. Under CO2 treatment, the 15N abundance of nitrate captured by resin bags was increased, which is most likely due to a effect of the N uptake by mycorrhiza.
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