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Eucalyptus clones are selected according to pro-ductivity, wood quality, rooting capacity, and resistance to drought, frost and diseases. However, kinetic and morpho-logical parameters that determine the absorption efficiency of nutrients such as nitrate (NO 3 ? ) and ammonium (NH 4 + ) are often not considered in breeding programs. The objective of this study was to evaluate the morphological, physiologi-cal and kinetic parameters of nitrogen uptake by clones of Eucalyptus saligna (32,864) and Eucalyptus grandis (GPC 23). Morphological parameters in shoot and root systems, biomass and N concentrations in different organs, photo-synthetic pigment concentrations, parameters of chlorophyll a fluorescence and photosynthetic rates were evaluated. Kinetic parameters, maximum absorption velocity ( V max ), Michaelis-Menten constant ( K m ), minimum concentration ( C min ) and influx ( I ) were calculated for NO 3 ? and NH 4 + in the two clones. E. grandis clone was more efficient in the uptake of NO 3 ? and NH 4 + , and showed lower K m and C min values, allowing for the absorption of nitrogen at low con- centrations due to the high affinity of the absorption sites of clone roots to NO 3 ? and NH 4 + . Higher root lengths, area and volume helped the E. grandis clone in absorption efficiency and consequently, resulted in higher root and shoot biomass. The E. saligna clone had higher K m and C min for NO 3 ? and NH 4 + , indicating adaptation to environments with higher N availability. The results of NO 3 ? and NH 4 + kinetic parame- ters indicate that they can be used in Eucalyptus clone selec- tion and breeding programs as they can predict the ability of clones to absorb NO 3 ? and NH 4 + at different concentrations.