Response of plant species to concentrations of zinc in solution. II. Rates of zinc absorption and their relation to growth

Abstract

Rates of zinc absorption by eight plant species grown for 46 days increased almost linearly from 2 to 400 ng atoms Zn/g fresh roots/day as zinc concentration in flowing culture solutions increased from 0.01 to 6.25µM At particular zinc concentrations, rates of absorption were about one-tenth of those reported for excised roots and up to 50 times greater than calculated rates of absorption from standard culture solutions. Reasons for these discrepancies arc discussed. At rates of zinc absorption of 2–4 ng atoms/g fresh roots/day many species developed symptoms of zinc deficiency and no species made maximal growth. Increasing rates of absorption to 10 ng atoms/g/day increased the growth of all species to maximal or near-maximal growth. Increasing rates of absorption beyond this slightly increased the yield of some species, but between 20 and 100 ng atoms/g/day there was no effect on the yield of any species. Rates in excess of 240 ng atoms/g/day were associated with depressed yields in all legumes but not in any cereals. Differences in rates of zinc absorption contributed to, but could not solely account for, differences among species in response to zinc concentrations in solution. The extent to which other factors may have modified the relationship between rate of absorption and yield is discussed.