|Da Silva, Ivo Ribeiro - NC STATE UNIV|
|Ferrufino, Armando - NC STATE UNIV|
|Sanzonowicz, Claudio - NC STATE UNIV|
|Smyth, Thomas - NC STATE UNIV|
Submitted to: Brazilian Soil Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 9, 2005
Publication Date: November 20, 2005
Citation: Da Silva, I., Ferrufino, A., Sanzonowicz, C., Smyth, T.J., Israel, D.W., Carter Jr, T.E. 2005. Interactions between magnesium, calcium, and aluminum on soybean root elongation. Brazilian Soil Sciences ('Revista Brasileira de Ciencia do Solo'). 29:747-754. Interpretive Summary: Soybean is grown extensively in subtropical and temperate areas such as the southeastern USA and the Cerrados in Brazil, where acid soils are prevalent and Al toxicity restricts root growth. Al toxicity can be corrected by liming, but this approach is not always economically feasible. Where liming is impractical, an economically and environmentally sound alternative is to develop cultivars which are Al tolerant. This approach has been used with some success in alfalfa and maize Al tolerance was first reported in soybean over 30 years ago Since then researchers have assessed genetic response in a number of test environments. At present, only moderate levels of Al tolerance have been detected in soybean. This lackluster success in soybean is due in part to imperfect screening methods. In that regard, very little is known about the combined effects of Al toxicity, magrnsium and calcium on the screening soy germplasm for Al tolerance. This problem is examined in the present paper.
Technical Abstract: Alleviation of Al rhizotoxicity by Ca and Mg can differ among species and genotypes. Root elongation of soybean [Glycine max (L.) Merr.] line N93-S-179 and cvs. Young and Ransom exposed to varying concentrations of Al, Ca and Mg were compared in two experiments using a vertically split root system. Roots extending from a surface compartment with limed soil grew for 12 days into a subsurface compartment with nutrient solution treatments maintained at pH 4.6 with either 0 or 15 µmol L-1 Al. Calcium and Mg concentrations in treatments ranging from 0 to 20 mmol L-1. Although an adequate supply of Mg was provided in the surface soil compartment for soybean top growth, an inclusion of Mg was necessary in the subsurface solutions to promote root elongation in both the presence and absence of Al. In the absence of Al in the subsurface solution, tap root length increased by 74 % and lateral root length tripled when Mg in the solutions was increased from 0 to either 2 or 10 mmol L-1. In the presence of 15 µmol L-1 Al, additions of 2 or 10 mmol L-1 Mg increased tap root length fourfold and lateral root length by a factor of 65. This high efficacy of Mg may have masked differences in Al tolerance between genotypes N93 and Young. Magnesium was more effective than Ca in alleviating Al rhizotoxicity, and its ameliorative properties could not be accounted for by estimated electrostatic changes in root membrane potential and Al3+ activity at the root surface. The physiological mechanisms of Mg alleviation of Al injury in roots, however, are not known.