Functional specialization of Eucalyptus grandis fine roots: contrasting potential uptake rates for nutrients in function of depth and soil fertility

Little is still known about the role of deep roots in the nutrition of forest. We then studied the potential uptake of N, K and Ca by Eucalyptus grandis trees (2 years of age), in Brazil, as a function of soil depth and fertilization. Our hypotheses were: i) deep roots are more efficient than the shallow roots in potassium and calcium uptake compared to nitrogen ii) the specialization of the eucalyptus roots in nutrient absorption decreases when soil fertility is improved by fertilization. We injected NO3 -15N, Rb+ (analog of K+) and Sr 2+ (analog of Ca 2+) tracers simultaneously in a solution at 10, 50, 150 and 300 cm in depth. A complete randomized design was set up with three replicates of paired trees per injection depth and soil fertility. Recently expanded leaves were sampled at 70 days after tracer injection. Determination of foliar Rb, Sr concentrations and 15N atom% makes it possible to estimate the relative uptake potential (RUP) from the 4 soil depths and the Specific RUP, defined as RUP, per unit of fine root length density in the corresponding soil layer. The results being analysed will give insights into the functional specialization of roots in forests.