Bioscience Evidence 2024, Vol.14, No.4, 154-160 http://bioscipublisher.com/index.php/be 156 temperature and humidity of 26.50 ℃-28.30 ℃ and 80.40%-87.60% respectively while that of afternoon was 30.60 ℃-34.90 ℃ and 69.40%-75.40%. There was one seedling per pot with each treatment replicated five times in a completely randomized design, and it lasted for 3 months. 2.3 Data collection Shoot length was measured using a meter rule from the soil level to the apical bud. Stem girth was determined using a digital vernier caliper (model 0-200 mm) at 10 cm point from the base of the stem. Leaf area was measured with leaf area meter (model LI-COR 300) of the first three fully expanded leaves. Leaves and roots on each plant were counted, and root length measured using a meter rule. Biomass was assessed through fresh and dry weight determinations. 2.4 Laboratory procedure and data analysis Dried plant samples were milled into fine powder and digested with 10 ml of 20% sulfuric acid. Pb and Zn concentrations were determined using spectrophotometer according to AOAC (1990). One-way Analysis of Variance was used for statistical analysis, and Tukey HSD test was performed to separate means where there were differences using the Statistical Package for Social Sciences (SPSS) version 24.0. This was used as it offered reliable and fast answers; effective in data management; didn't require a lot of effort to use the software; and easy to use for quantitative data analysis. 3Results 3.1 Soil used for planting The soil used for planting had 5.60 pH, 6.19% clay, 4.29% silt, 89.7% sand, 2.89% C, 0.14% N, 9.02 mg/100 g P, 6.24 mg/100g Ca, 1.84 mg/100 g Mg, 0.34 mg/100 g Na, 0.23 mg/100 g K, 0.20 mg/100 g H, 8.86 mg/100 g CEC, 0.14 mg/kg Pb and 3.56 mg/kg of Zn. 3.2 Plant survival and growth All plants survived the heavy metal concentrations applied, and there was no significant effect of Pb on number of leaves at 20-60 mg/kg but significantly increased it at 80-100 mg/kg compared to the control (Table 1). Number of leaves of plants grown in Zn-contaminated soil was significantly reduced at all the concentrations applied, in comparison to the control. Statistical analysis revealed that stem girth of plants grown with Pb contamination was not significantly impacted compared to the control. However, Zn contamination led to a significant reduction of stem girth at 60-100 mg/kg. Soil contamination with Pb did not significantly affect leaf area except at 80 mg/kg where an increase was recorded relative to the control. Leaf area of plants grown under Zn contamination did not, however, differ significantly from those grown in soil free of heavy metals. Pb and Zn decreased root length without statistical difference from the control while number of roots was not significantly impacted by the metals. Table 1 Effect of soil contamination with Pb and Zn on growth parameters of Chromolaena odorata Growth parameter Heavy metal Heavy metal concentration in soil (mg/kg) 0 20 40 60 80 100 Number Pb 47.50+9.26b 37.10+3.42b 40.00+1.00b 50.50+3.62b 107.70+17.66a 76.20+11.85a of leaves Zn 43.70+1.47a 29.70+2.98b 28.00+1.31b 28.00+1.41b 22.70+1.00b 19.50+2.73c Plant Pb 82.07+4.95b 96.00+12.43b 79.03+4.09b 92.85+4.17ab 125.30+8.21a 110.70+10.54a height (cm) Zn 84.16+4.84b 98.00+11.32b 81.03+4.09b 94.74+4.06ab 127.30+8.10a 112.70+10.43a Stem Pb 14.10+1.35a 12.64+2.0.37a 13.22+0.57a 15.70+0.55a 16.00+1.94a 18.30+1.03a girth (cm) Zn 16.30+0.72a 17.00+2.06a 17.20+1.27a 11.80+0.34b 10.48+0.91b 10.88+0.39b Leaf Pb 54.50+11.12b 33.10+3.37b 58.00+5.46b 52.00+15.29b 107.00+13.52a 87.00+11.00ab area (cm2) Zn 49.50+3.45a 48.70+3.41a 55.30+1.49a 48.70+4.01a 38.00+1.60ab 37.00+2.63ab Root Pb 39.22+14.21a 28.70+2.76a 26.10+4.63a 29.50+4.63a 34.10+4.61a 24.40+3.51a length (cm) Zn 57.44+18.43a 46.91+4.59a 44.30+6.85a 47.70+3.77a 51.30+6.82a 42.60+4.73a Number Pb 5.44+0.44a 5.10+0.35a 4.10+0.34a 5.30+0.82a 5.50+0.57a 5.00+0.71a of roots Zn 6.79+2.23a 6.20+0.48a 5.30+0.47a 6.50+1.03a 6.70+0.79a 6.00+0.93a 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)
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