Nutrient uptake of soybean genotypes under aluminum toxicity

Abstract

The objective of this research was to study the nutrient uptake of soybean exposed to aluminium (Al) toxicity. The factorial design consisted of two treatments arranged in a randomized block design with three replications. Liming was the first factor which consisted of four levels, i.e. i) without liming; ii) liming with 0.5×Al(exchangeable/ec); iii) liming with 1×Al(ec); and iv) liming with 1.5×Al(ec). Five genotypes were used as second factor, i.e. three tolerant genotypes (W3898-14-3, Wilis, and Kawi), and two sensitve genotypes (MLG 3209 and MLG 3083). It was found that two tolerant genotypes, W3898-14-3 and Kawi, had a higher potassium (K) and sodium (Na) uptake than susceptible genotypes. Liming affected significantly the ratio of Al/[calcium (Ca) + magnesium (Mg)] in roots and leaves, the content of Ca and Mg in the roots and the content of Mg in the leaves. The K content in the roots and the content of Ca, K, and Na in the leaves were unresponsive to the alteration of pH and Al saturation. IntroductionAmong the earth's crust minerals, aluminum (Al) is the third most abundant after oxygen and silicon (Bhalerao and Prabu, 2013). It can have a toxic effect on plants under specific soil conditions, especially when the soil is acid. The root is the plant organ most affected by Al toxicity, before the upper part organs (Meriño-Gergichevich et al., 2010). However, some plants can tolerate Al toxicity, whereas other cannot tolerate it at all. This suggests that there is a specific mechanism associated with Al toxicity tolerance. Al-tolerant plants can be classified in three groups according to the plant tissues that accumulate Al (Foy, 1984). The first group includes plants in which the Al concentration in the leaves is not always different from that of sensitive plants and remains at lower levels. The second group includes plants with no Al in the leaves and/or Al trapped in the roots. The third group includes plants in which Al tolerance is directly related to Al accumulation in the upper part of the plant. These plants have therefore a high internal tolerance towards Al. In principle, the mechanisms of Al tolerance facilitate Al exclusion from the root and/or confer the plant the ability to tolerate it in its organs (Vardar and Unal, 2007). Watanabe and Osaki (2002) proposed other Al toxicity tolerance mechanisms by classifying plant into two groups. The first group includes the Al excluders, i.e. plants that exclude Al from their organs. The second group includes the Al accumulators, i.e. the plants that inactivate Al in their organs. Al accumulator plants present specific mechanisms involved in tolerance, such as the immobilization of Al in the cell wall, cytoplasmic Al complexation by organic acids, vacuolar isolation of Al tolerant enzymes, and isolation of Al in the vacuoles (Sopandie et al., 2000). Inorganic nutrients are also involved in this mechanism due to the interaction of Al with other nutrients to form inactive molecules. When Al concentration increases, the concentrations of magnesium ...