Bioscience Evidence 2024, Vol.14, No.4, 154-160 http://bioscipublisher.com/index.php/be 157 3.3 Plant biomass Values of fresh and dry weights of plant parts were higher in those exposed to Pb and Zn than the control with the highest values recorded at 80 mg/kg (Table 2). Meanwhile, statistical analysis showed that the increase was significant at 80-100 mg/kg for leaf and stem, and at 80 mg/kg only for root. Table 2 Effect of soil contamination with Pb and Zn on biomass parameters of Chromolaena odorata Biomass parameter Heavy metal Plant part Heavy metal concentration in soil (mg/kg) 0 20 40 60 80 100 Fresh weight (g) Pb Leaf 38.90+5.21b 55.72+2.30b 51.03+17.09b 65.47+21.72b 141.31+65.48a 77.84+39.09a Stem 14.82+3.32b 25.39+5.68b 17.11+4.32b 60.27+31.77b 124.51+92.74a 29.32+10.04b Root 15.56+7.56b 26.57+4.13b 15.81+6.26b 50.40+34.51ab 70.41+48.07a 23.06+8.50b Zn Leaf 36.89+4.10b 53.61+2.57ab 49.92+16.98ab 63.36+20.61ab 83.20+29.03a 75.63+28.18a Stem 11.71+2.21b 22.28+4.57b 15.00+3.24b 57.16+21.64a 75.40+31.63a 44.20+9.13a Root 13.45+6.45b 24.46+3.02b 14.70+5.15b 48.39+33.40a 68.30+37.19a 21.95+7.49b Dry weight (g) Pb Leaf 15.62+7.64b 32.57+6.69b 33.21+13.51b 20.07+8.36b 69.63+24.55a 60.15+31.84a Stem 6.00+3.40b 14.35+5.11b 5.74+2.47b 12.83+4.42b 34.07+21.34a 13.24+7.16b Root 5.97+0.55b 13.65+2925b 4.71+1.81b 23.49+16.00a 39.29+30.38a 13.60+5.43b Zn Leaf 14.51+6.53b 29.46+5.85b 30.10+12.40b 20.41+7.25b 66.52+21.42a 57.04+28.73a Stem 5.02+2.32b 11.24+4.00ab 4.63+2.06b 18.72+3.33a 22.96+10.23a 12.13+6.05ab Root 5.65+0.51b 12.54+2.62b 6.68+1.98b 20.36+11.03a 36.18+20.27a 10.50+4.32b Note: Values are mean + standard error of 5 replicates. Means with the same letter(s) in superscript on the same row are not significantly different at p>0.05 (Tukey HSD Test) 3.4 Pb and Zn accumulation in plant parts Table 3 reveals that there were significantly higher concentrations of Pb and Zn in parts of plants grown in metal contaminated soil compared to the control treatment. According to the data, Pb in the leaf (28.50-54.50 ppm), stem (5.50-26.00 ppm) and root (5.50-26.50 ppm) were significantly more than their respective control values of 3.00, 0.01 and 1.50 ppm. Likewise, Zn concentrations were significantly higher in the leaf (35.00-36.50 ppm), stem (11.00-16.00 ppm) and root (19.00-27.50 ppm) than the control values at 3.00, 2.00 and 2.00 ppm respectively. Metal concentrations in plant parts increased with increasing level of soil contamination, with more accumulation in the leaf than other plant parts. Table 3 Concentrations (ppm) of Pb and Zn in plant parts of Chromolaena odoratagrown in soil contaminated with the heavy metals Heavy metal Plant part Heavy metal concentration in soil (mg/kg) 0 20 40 60 80 100 Pb Leaf 3.00b 28.50a 35.50a 37.00a 46.00a 54.50a Stem 0.01c 5.50b 17.50a 19.50a 20.50a 26.00a Root 1.50c 5.50b 8.50b 19.00a 22.50a 26.50a Zn Leaf 3.00b 35.00a 26.50a 25.50a 37.50a 36.50a Stem 2.00b 11.00a 10.00a 8.50a 10.50a 16.00a Root 2.00b 19.00a 31.00a 22.50a 20.00a 27.50a Note: Values are mean + standard error of 3 replicates. Means with the same letter(s) in superscript on the same row are not significantly different at p>0.05(Tukey HSD Test) 4 Discussion The soil was relatively free of heavy metal contamination as the baseline values were 0.14 mg/kg Pb and 3.56 mg/kg Zn before addition of heavy metals to the soil. The values correspond with records on Pb and Zn concentrations in uncontaminated soils from South West, Nigeria according to Adeyi and Babalola (2017) as well as Patinvoh et al. (2021). The presence of Pb and Zn in the soil stimulated growth of C. odorata. For instance, according to Islam et al. (2024), zinc is an important component of various enzymes that are responsible for driving many metabolic reactions in all crops. Growth and development would stop if specific enzymes were not present in plant tissue. Carbohydrate, protein, and chlorophyll formation is significantly reduced in zinc-deficient
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