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ARS Home » Southeast Area » Raleigh, North Carolina » Soybean and Nitrogen Fixation Research » Research » Publications at this Location » Publication #211325
Title: Soybean Root Elongation Response to Magnesium Additions to Acid Subsoil

Author
item HASHIMOTO, YOHEY - N.C. STATE UNIV
item SMYTH, T.JOT - N.C. STATE UNIV
item Israel, Daniel
item HESTERBERG, DEAN - N.C. STATE UNIV

Submitted to: Journal of Plant Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/2/2008
Publication Date: N/A
Citation: N/A

Interpretive Summary: This study tested the concept that magnesium enhances root elongation in the presence of rhizotoxic aluminum by stimulating the roots to produce an aluminum chelator, citrate, in hydroponics in a situation more closely related to field conditions (soil columns in the greenhouse). In the soil system addition of magnesium did not enhance tolerance of root elongation to aluminum even though magnesium was limiting in the unamended soil. Citrate adsorption experiments showed that that citrate produced by the roots was either adsorbed by the soil or biodegraded in the soil. This work clearly demonstrates that results from hydroponic studies need to be verified under conditions more representative of the field.

Technical Abstract: Additions of micromolar concentrations of Mg2+ to hydroponic solutions enhance Al tolerance of soybean [Glycine max (L.) Merr.] by increasing citrate secretion from roots and external complexation of toxic Al species in solution. The objective of this study was to assess the ameliorative effect of Mg additions on soybean root elongation into acid subsoils in a split-root system. Roots of soybean Plant Introduction 416937 seedlings extending from a limed surface soil compartment grew for 28 days into a subsurface compartment containing acid subsoil samples from Cecil (oxidic and kaolinitic), Creedmoor (montmorillonitic) and Norfolk (kaolinitic) soil series. Subsoils in the subsurface compartment had three Mg treatments consisting of their native equilibrium soil solution concentrations (50 or 100 'M) and MgCl2 additions to achieve initial concentrations of 150 and 300 'M Mg (Mg150 and Mg300, respectively). Root elongations into Mg-treated subsoils were compared with a CaCO3 treatment limed to achieve a soil pH value of 6. Root length for the treatments without added Mg or lime decreased in the order of the Cecil, Norfolk and Creedmoor subsoils, and corresponded to the order of increasing percent Al saturation (27, 61 and 83%, respectively). Root growth in the subsurface compartment and aboveground dry matter responses to the Mg treatments were less than for the lime treatments, and there were no differences between the Mg150 and Mg300 treatments as compared to the treatments without added Mg or lime. Citrate adsorption experiments revealed that over 66% of citrate added to the subsoils was either adsorbed or biodegraded, suggesting that most of the root secreted citrate in the soil would be unavailable to complex Al and ameliorate rhizotoxicity.