Protective effect of divalent cations against aluminum toxicity in soybean

Abstract

SUMMARYA 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 CaCl 2 or MgCl 2 (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 (CaCO 3 ) 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 Uma grande parte da soja no Brazil é cultivada atualmente na região do Cerrado, e é nessa região que ocorre a maior expansão da cultura. Nessa região, a maioria dos solos é ácida e, geralmente, apresenta níveis elevados de alumínio (Al) tóxico. Portanto, é importante compreender como determinados cátions reduzem a rizotoxidez de Al em plantas de soja. Neste estudo foram avaliados, em solução nutritiva, o efeito protetor de nove cátions divalentes (Ca, Mg, Mn, Sr, Sn, Cu, Zn, Co and Ba) contra a rizotoxidez de Al e o efeito positivo do Ca e Mg no crescimento das plantas de soja num solo com elevada saturação por Al. A relação entre Ca e Mg trocáveis foi variada por meio de adição de diferentes quantidades de CaCl 2 ou MgCl 2 (com as proporções variando entre 100:0 até 0:100), sem que ocorresse alteração no pH do solo. Tratamentos testemunhas consistiram de solo sem aplicação ou com aplicação de calcário (CaCO 3 ). Foi observado que, na ausência do Al, os cátions Cu, Zn, Co e Sn foram tóxicos mesmo em baixas concentrações (25 μmol L -1 ), enquanto Mn, Ba, Sr e...

Chemical Species and Aluminum Concentration in the Solution of Acid Soils Cultivated with Soybean and Corn under Liming

“…Simple determination of the exchangeable Al contents in the soil or the total Al in the soil solution is not a sufficient indicator to evaluate the toxicity of this element to plants. To make this evaluation, quantification of the chemical species considered toxic becomes necessary, mainly the labile species of Al, such as Al 3+ , Al(OH) 2+ , and Al(OH) 2 + , as well as non-toxic species, especially the complexes of Al with organic and inorganic molecules that alter the proportion and activity of the toxic forms of Al (Ferro-Vásquez et al, 2014;Hagvall et al, 2015;Nolla et al, 2015) and, furthermore, the elements that can reduce Al toxicity, such as Ca 2+ and Mg 2+ (Silva et al, 2008;Hashimoto et al, 2010;Auxtero et al, 2012). In general, Al 3+ activity, rather than measurements of the soluble or exchangeable forms, is the best indicator of toxicity potential in acid soils (Ferrufino et al, 2000;Spera et al, 2014).…”

Nutrient uptake of soybean genotypes under aluminum toxicity

“…On the contrary, the binding of Al 3+ to negative charges and the precipitation of Al in the apoplast may decrease the loading of Mg 2+ ions (Bose et al, 2011). The effect of Mg is ion-specific and is not only associated to an electrostatic protection mechanism (da Silva et al, 2008). Being a cation, K can also potentially decrease Al toxicity.…”

Crescimento e estado nutricional da soja influenciados pela relação Ca:Mg em solo do cerrado paraense

“…Em razão dos baixos teores de cálcio (Ca) e magnésio (Mg) nos solos, não só a quantidade aplicada visando à correção é importante, mas também a relação entre esses nutrientes, visto que competem pelos sítios de troca no solo e na absorção pelas raízes (MOREIRA et al, 2003;SILVA et al, 2008).…”