The spatial distribution of phosphate in the root system modulates N metabolism and growth in Eucalyptus grandis young plants

Abstract

High P homogeneously applied in roots reduced growth and nitrate uptake. High P in a patch reduced N in tissues but did not reduce growth, because root hydraulic conductivity increased. Little is known about consequences of nutrient imbalances, i.e., when the increase of one nutrient’s availability, in non-toxic concentration, reduces plant growth, because other nutrient availability is low. In a soil with low N (nitrogen) availability, high homogeneous P (phosphorus) availability reduced nitrate uptake and reduced growth of Eucalyptus grandis plants. However, if the same availability of P was applied only in a part of the root system (localized), no depressive effect was observed. In this work, it was analyzed which step in the early assimilation of N was affected by high homogeneous P and how localized P counteracted this depressive effect. Inorganic forms of N and protein in plant tissues as well as some plant hydraulic traits were analyzed in an experiment with E. grandis plants growing in perlite in a split-root system fed with low N. Control plants received low P. High P was applied in two spatial distributions: localized in one part of the root system (LP) or distributed homogeneously in both parts (HP). HP reduced growth, while LP had no depressive effect in growth. Both high P spatial distributions reduced concentration of nitrate in roots. Since concentration of nitrate in the xylem was similar in all treatments and nitrate in leaves was lower in high P than in control treatment, the reduction in root N was probably due to lower uptake. Nevertheless, plants growing with LP had no depressive effect in growth, because the decrease in N assimilation was counteracted by an increase of root hydraulic conductivity.