Abstract
A large proportion of soybean fields in Brazil are currently cultivated in the Cerrado region, where the area planted with this crop is growing considerably every year. Soybean cultivation in acid soils is also increasing worldwide. Since the levels of toxic aluminum (Al) in these acid soils is usually high it is important to understand how cations can reduce Al rhizotoxicity in soybean. In the present study we evaluated the ameliorative effect of nine divalent cations (Ca, Mg, Mn, Sr, Sn, Cu, Zn, Co and Ba) in solution culture on Al rhizotoxicity in soybean. The growth benefit of Ca and Mg to plants in an acid Inceptisol was also evaluated. In this experiment soil exchangeable Ca:Mg ratios were adjusted to reach 10 and 60 % base saturation, controlled by different amounts of CaCl2 or MgCl2 (at proportions from 100:0 up to 0:100), without altering the soil pH level. The low (10 %) and adequate (60 %) base saturation were used to examine how plant roots respond to Al at distinct (Ca + Mg)/Al ratios, as if they were growing in soils with distinct acidity levels. Negative and positive control treatments consisted of absence (under native soil or undisturbed conditions) or presence of lime (CaCO3) to reach 10 and 60 % base saturation, respectively. It was observed that in the absence of Aluminum, Cu, Zn, Co and Sn were toxic even at a low concentration (25 µmol L-1), while the effect of Mn, Ba, Sr and Mg was positive or absent on soybean root elongation when used in concentrations up to 100 µmol L-1. At a level of 10 µmol L-1 Al, root growth was only reverted to the level of control plants by the Mg treatment. Higher Tin doses led to a small alleviation of Al rhizotoxicity, while the other cations reduced root growth or had no effect. This is an indication that the Mg effect is ion-specific and not associated to an electrostatic protection mechanism only, since all ions were divalent and used at low concentrations. An increased exchangeable Ca:Mg ratio (at constant soil pH) in the acid soil almost doubled the soybean shoot and root dry matter even though treatments did not modify soil pH and exchangeable Al3+. This indicates a more efficient alleviation of Al toxicity by Mg2+ than by Ca2+. The reason for the positive response to Mg2+ was not the supply of a deficient nutrient because CaCO3 increased soybean growth by increasing soil pH without inducing Mg2+ deficiency. Both in hydroponics and acid soil, the reduction in Al toxicity was accompanied by a lower Al accumulation in plant tissue, suggesting a competitive cation absorption and/or exclusion of Al from plant tissue stimulated by an Mg-induced physiological mechanism.
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Claims 10
Claim · model-written summary
Cu, Zn, Co and Sn were toxic without aluminum at 25 µmol L-1.
- Taxon
- soybean
Glycine maxt0 - Treatment
- Cu, Zn, Co and Sne0
- Outcome
- toxice0
- Direction
- toxice0
- Value
- 25 µmol L-1e0
- Comparator
- absence of Aluminume0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“in the absence of Aluminum, Cu, Zn, Co and Sn were toxic even at a low concentration (25 µmol L-1)”
t0“soybean”
Claim · model-written summary
Mn, Ba, Sr and Mg had positive or absent effects on soybean root elongation up to 100 µmol L-1.
- Taxon
- soybeanGlycine maxe0
- Treatment
- Mn, Ba, Sr and Mge0
- Outcome
- soybean root elongatione0
- Direction
- positive or absente0
- Value
- 100 µmol L-1e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the effect of Mn, Ba, Sr and Mg was positive or absent on soybean root elongation when used in concentrations up to 100 µmol L-1”
Claim · model-written summary
At 10 µmol L-1 aluminum, only Mg restored root growth to control levels.
- Taxon
- soybeanGlycine maxt0
- Treatment
- Mg treatmente0
- Outcome
- root growthe0
- Direction
- revertede0
- Qualifier
- 10 µmol L-1 Ale0
- Comparator
- control plantse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“At a level of 10 µmol L-1 Al, root growth was only reverted to the level of control plants by the Mg treatment”
t0“soybean”
Claim · model-written summary
Higher tin doses slightly alleviated aluminum rhizotoxicity.
- Taxon
- soybeanGlycine maxt0
- Treatment
- Higher Tin dosese0
- Outcome
- Al rhizotoxicitye0
- Direction
- alleviatione0
- Qualifier
- smalle0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Higher Tin doses led to a small alleviation of Al rhizotoxicity”
t0“soybean”
Claim · model-written summary
Other cations reduced root growth or had no effect.
- Taxon
- soybeanGlycine maxt0
- Treatment
- other cationse0
- Outcome
- root growthe0
- Direction
- reducede0
- Qualifier
- or had no effecte0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the other cations reduced root growth or had no effect”
t0“soybean”
Claim · model-written summary
Increasing exchangeable Ca:Mg ratio nearly doubled soybean shoot and root dry matter at constant soil pH.
- Taxon
- soybeanGlycine maxe0
- Treatment
- increased exchangeable Ca:Mg ratioe0
- Outcome
- soybean shoot and root dry mattere0
- Direction
- almost doublede0
- Qualifier
- constant soil pHe0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“An increased exchangeable Ca:Mg ratio (at constant soil pH) in the acid soil almost doubled the soybean shoot and root dry matter”
Claim · model-written summary
Mg2+ alleviated aluminum toxicity more efficiently than Ca2+.
- Taxon
- soybeanGlycine maxt0
- Compound
- Mg2+e0
- Outcome
- Al toxicitye0
- Direction
- more efficient alleviatione0
- Comparator
- Ca2+e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“This indicates a more efficient alleviation of Al toxicity by Mg2+ than by Ca2+”
t0“soybean”
Claim · model-written summary
CaCO3 increased soybean growth by increasing soil pH.
- Taxon
- soybeanGlycine maxe0
- Treatment
- CaCO3e0
- Outcome
- soybean growthe0
- Direction
- increasede0
- Qualifier
- increasing soil pH without inducing Mg2+ deficiencye0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“CaCO3 increased soybean growth by increasing soil pH without inducing Mg2+ deficiency”
Claim · model-written summary
Reduced aluminum toxicity coincided with lower aluminum accumulation in plant tissue.
- Taxon
- soybeanGlycine maxt0
- Compound
- Ale0
- Outcome
- Al accumulation in plant tissuee0
- Direction
- lowere0
- Qualifier
- reduction in Al toxicitye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the reduction in Al toxicity was accompanied by a lower Al accumulation in plant tissue”
t0“soybean”
Claim · model-written summary
The authors suggest Mg-induced absorption competition or exclusion explains lower tissue aluminum.
- Taxon
- soybeanGlycine maxt0
- Outcome
- exclusion of Al from plant tissuee0
- Qualifier
- competitive cation absorption and/or exclusion of Al from plant tissue stimulated by an Mg-induced physiological mechanisme0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“suggesting a competitive cation absorption and/or exclusion of Al from plant tissue stimulated by an Mg-induced physiological mechanism”
t0“soybean”
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Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.