Root Uptake and Partition of Copper, Iron, Manganese, and Zinc in Pinus radiata Seedlings Grown under Different Copper Supplies

Abstract

Summary In spite of the low Cu needs, a Cu2+ level of 0.03 µM in hydroponic cultures of Pinus radiata seedlings induces a Cu-deficient situation; under these conditions the foliar Cu was 4 mg·kg-1 dry wt after 2.5 months growth, which decreased to 1 mg kg-1 in 5-month-old seedlings. This is shown by a decrease of the growth rate with time, which appears negligible between 7.5 and 9 months in culture. The Cu content of roots, foliar and non-foliar stems, and leaves increases with the micronutrient concentration in the culture solutions, but the response of each organ is inversely related with its distance from the hydroponic medium. In any case P. radiata seedlings showed a very efficient Cu2+ absorption capability of the root, but the nutrient translocation to the aerial organs appears restricted, maybe as a protection mechanism. Until 7.5 months in culture the optimum plant development occurs under excess Cu2+, which shifts to normal Cu2+ levels after 9 months growth; this can be explained as a transient Cu deficiency during the first developmental stage. Mn absorption showed some type of antagonism with that of Cu2+, the needles being the site of the highest Mn concentration in pine. On the contrary, the rate of Fe absorption increases with Cu2+ levels, but the translocation to stems and leaves occurs very slowly. Zn showed a Z-shape partition pattern along root, stems, and needles, with the highest concentrations in root and foliar stem; in addition, Zn absorption appears to be antagonistic to that of Cu.