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Potassium and sodium supply effects on the adjustments to water deficit of Eucalyptus grandis trees: insights from a throughfall exclusion experiment in Brazil

Laclau J.P., Battie Laclau P., Christina M., Gonçalves J.L.M., Epron D., Moreira R.M., Le Maire G., Bouillet J.P., Cabral O.M.R., Nouvellon Y.. 2014. International Forestry Review, 16 (5) : p. 237-238. IUFRO World Congress. Sustaining Forests, Sustaining People: The Role of Research. 24, 2014-10-05/2014-10-11, Salt Lake City (Etats-Unis).

Identifying management practices enhancing tree tolerance to drought and nutrient deficiencies is of primary interest to confront global change. A split-plot design with 3 blocks was set up to gain insight into the interactions between fertilization and water stress on carbon, water and nutrient cycling in Eucalyptus plantations on deep tropical soils. The main-plot factor was the water supply (undisturbed vs exclusion of 37% of throughfall) and the sub-plot factor compared 3 fertilization regimes (control, sodium supply, potassium supply). Biomass and nutrient accumulations in tree components, leaf area index (LAI), fi ne root development, leaf gas exchanges, soil respiration, soil solution chemistry as well as soil water contents down to the water table at 17 m in depth have been measured over the fi rst half of the rotation. The MAESPA model was used to estimate the contribution of water withdrawn in deep soil layers over 3 years. Carbon labelling for 12 trees at age 2 years showed a strong influence of potassium addition on phloem sap velocity and C allocation patterns. Although potassium supply improved stomatal sensitivity to water defi cit, the great enhancement in growth exacerbated tree water defi cit during dry periods. The behavior of sodium-supplied trees was intermediate. Fertilization regimes should be revisited in a context of climate change for optimizing the trade-off between safety and growth.

Mots-clés : eucalyptus grandis; déficit hydrique du sol; déficit pluviométrique; carence du sol; stress dû à la sécheresse; fertilisation; sodium; potassium; brésil

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