Relationships between physiological and morphological attributes related to phosphate uptake in 25 genotypes of Arabidopsis thaliana

The degree of genetic integration among morphological and physiological characters associated with phosphate uptake in impoverished versus fertile sites was studied among 25 inbred homozygous lines of Arabidopsis thaliana (L.) Heynh. The characters recorded were initial uptake rates, Cmin (which reflects the ability to deplete phosphate to low concentrations), SRL (specific root length), and root: shoot allocation variables. Highly significant genotypic differentiation was detected for all of the variables (P < 0.001). Cmin was correlated with influx per cm or mg of root; the lines better able to pick up Pi at low concentrations generally had slower initial uptake rates per cm or mg of root. This suggests an evolutionary divergence between a character important for nutrient uptake under fertile conditions, and one important for nutrient uptake under impoverished conditions. This relationship however, may not be valid due to the non-proportional relationship between root length or mass and influx. With a measure of influx that took this non-proportionality into account, the relationship became nonsignificant. SRL was negatively correlated (P< 0.05) with influx per unit length of root. This suggests that there is an allocation-based trade-off between root length and diameter among Arabidopsis thaliana genotypes. Lower uptake rates per unit length of root for genotypes with thin roots may simply be a consequence of lower root surface area.