Effect of Lead Polution on the Performance and Protein Content of Two Soybean Varieties

摘要

Pollution by lead has been classified as being harmful to plants and animals because it accumulates in organisms and bio-magnifies in the food chain. Excessive concentration of lead in plants results in phyto-toxicity of the cell membrane. It has become necessary to determine the effect of lead, on the yield performance (number of leaves, plant height and yield) and protein content of two soybean varieties, TGX 1485-ID (VI) and TGX 1740-2F (V2). The soybean varieties were planted in 4x2 factorial designs. The experiment consisted: Uncontaminated soil (control) and three contaminated soils containing 300, 600 and 1,800 mg Pb L-1. The soil had the following characteristics: pH 6.1, organic matter 6.68% and CEC 11.24 cmol kg-1. Per cent uptake in lead content of the contaminated soils ranged from 65.25 to 81.94 in V1 and 66.20 to 82.18 in V2 after harvest. This indicated variable decrease in lead levels in contaminated soils while lead was not detectable in the planted and harvested seeds. The mean germination and maturity days of variety TGX 1485-ID were 4.63±0.14 and 110.5±0.11 while it was 4.88±0.13 and 105.5±1.23 in variety TGX 1740-2F, respectively. There were no significant difference in the various lead contamination levels with respect to germination days and maturity days. The mean stem heights of VI were 49.5±1.11, 39.9±0.25, 43.9±1.01 and 44.1±1.21 cm while 43.6±1.31, 47.3±0.42 and 45.3±0.42 cm were obtained in V2 at Control, 300, 600 and 1500 mg L-1 treatment levels, respectively. Comparison of the plant height between the TGX 1485-1D variety (V1) and the TGX 1740-2F (V2) variety showed that there was no significant difference (p>0.05) between the two varieties with regards to plant height. The mean number of leaves in V1 were 52.4±0.16, 50.6±1.14, 48.4±1.67 and 48.4±0.15 while 51.4±1.26, 48.6±0.33, 45.3±0.25 and 52.3±0.17 were for V2 at the control, 300g L-1, 600 mg L-1 and 1800 mg L-1, treatment levels, respectively. However, lead affected the number of leaves significantly between (p<0.05) the two soybean varieties. At the four lead treatment levels, the mean pod weights (gram) ranged from 3.55?2.22 to 5.23?1.03 in TGX1485-D and 4.52?1.16 to 5.30?0.41 in TGX1740-2F. There were no significant differences (p>0.05) in the number of pods and pod dry weights of the varieties and within their treatments. Spiking of the soil with lead at various concentrations did not have appreciable effect on the soybean protein contents of the two varieties after harvest. This study showed that lead though absorbed from the soil was not accumulated in the leaves and seeds of the two soybean varieties indicating that the risk of lead entering the food chain through these media remains minimal.