EXPERIMENTAL APPROACH TO ALUMINUM PHYTOTOXICITY

Soil acidity is a serious agricultural problem throughout large geographic areas of the world, possibly affecting as much as 40% of the world's arable soils. Plants growing on acid soils suffer from a number of detrimental factors, including nutrient deficiencies, drought intolerance, and Mn toxicity. Aluminum toxicity, however, has been identified as one of the more important growth-limiting factors on acid soils. The intense research effort addressing; basic and applied aspects of Al phytotoxicity reflects the agronomic and economic importance of the acid soil-Al problem. In the first stage of this study, several 21-day-old lettuce plants (Lactuca sativa L.) were transplanted from normal soil (pH 6.8, exchangeable Al 0.11 meq/100 g soil) to an acid soil (pH 3.8, exchangeable Al 10 meq/100 g soil). Following that, the lettuce plants were collected at random at different times over a period of 14 days and the Al, Ca, and K contents were determined in both roots and leaves by means of atomic absorption spectrometry. Results indicated that plants grown in the acid soil accumulate considerable amounts of Al, especially in the roots, where the loss of cations was more evident. In comparison with the "blank plants," a reduced growth was also noted. In a second stage of the study, the lettuce plants from normal soil were allowed to grow in nutrient solutions having different Al concentrations, namely 2, 10, and 50 mM. Sample collection was performed after 2, 4, 8, 24, and 48 h, respectively. Aluminum, Ca, K, and Mg were determined as described above. In roots, high accumulation factors of aluminum were quickly obtained but the decrease of Ca seemed to be lower than that observed in the first model. In the leaves, the intake of Al was less and the changes in cation concentrations were limited and constant in all solutions. © 1992.