Soybean Response to Mn Added in EDTA- or CDTA-Buffered Nutrient Solution

ADDITION of chelating agents can increase Mn2+ activity (pMn2+).
in soil solution and thus increase Mn uptake and plant growth. This
study aimed at evaluating soybean growth and Mn2+ uptake in
ethylenediaminetetraacetic acid (EDTA), or trans- 1,2-diamineciclohexane-
tetracetic acid (CDTA) buffered nutrient solution. Varied
levels (0.1, 0.32, 1.00, 3.16, 10.0 and 32.0 μM) of Mn, while constant
concentrations of all other micronutrients, in combination with EDTA, or
CDTA were imposed to soybean (Glycine max L.Merr.) in solutions with
pH 6.0.
Plant dry matter (DM) increased with increasing activity, not the total
concentration of Mn and was highest at pMn2+ 8.0-8.1 in EDTA- and
CDTA-buffered solutions. With pMn2+ >8.0, plant leaves accumulated
higher Mn2+, but 80-87 mg Mn2+ kg-1 DM seemed sufficient for optimum
plant growth. With pMn2+ < 8.0, the concentration remained at the
optimum level in the CDTA-buffered solution, whereas in the EDTAbuffered
solution leaf Mn2+ concentration was in the range 193-241 mg
Mn2+ kg-1 DM. At pMn2+ < 8.0, leaf Ca2+ and Mg2+ were higher with
MnCDTA than with MnEDTA. Leaf Fe3+ concentration remained
constant and did not significantly change in response to Mn availability.
Fe: Mn ratio decreased with increasing Mn availability in the EDTA and
CDTA solutions.
CDTA-buffered solution offers a strong control of plant uptake of
Mn2+ due to its strong control of the free concentrations of Mn2+, Ca2+
and Mg2+ under conditions of limited Mn availability.