Morphological and kinetic parameters of the absorption of nitrogen forms for selection of Eucalyptus clones

Eucalyptus clones are selected according to productivity, wood quality, rooting capacity, and resistance to drought, frost and diseases. However, kinetic and morphological 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, physiological 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, photosynthetic 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 concentrations 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 parameters indicate that they can be used in Eucalyptus clone selection and breeding programs as they can predict the ability of clones to absorb NO 3 − and NH 4 + at different concentrations.