Ecology of Iranian Forest

Extended Abstract

Background: The accumulation of cadmium (Cd) in soil is a pressing environmental issue, recognized as one of the most toxic pollutants affecting terrestrial ecosystems. Cadmium can significantly reduce microbial activity and soil fertility, ultimately leading to the death of plants. This problem has raised global concerns due to its widespread occurrence and detrimental effects on agricultural productivity and ecosystem health. The present study aims to investigate the resistance of male (clone 62-167) and female (clone 62-149) individuals of black poplar (Populus nigra L.) to cadmium exposure. By examining various vegetative and physiological characteristics, this research seeks to provide insights into the potential for utilizing these clones in afforestation efforts on Cd-contaminated soils.
Methods: To achieve the study's objectives, a greenhouse experiment was designed following a randomized complete block design. This design incorporated two main factors: cadmium concentration (with levels of 0, 50, 150, and 200 mg/kg of soil) and gender (male and female clones of black poplar). The experiment was conducted over a period of 120 days, providing ample time to assess the impacts of cadmium on the seedlings. The physiological variables measured included net photosynthesis rate, transpiration rate, stomatal conductance, water use efficiency, water potential, mesophilic conductance, and intracellular CO2 concentration. In addition, several vegetative characteristics were evaluated, such as root collar diameter growth, height growth, total biomass, and leaf area. The stress treatment commenced in late May, where seedlings were irrigated weekly with a cadmium salt solution for the first five weeks. This approach ensured that the plants were exposed to cadmium in a controlled manner. Following this initial stress period, the seedlings were irrigated with rainwater, respecting the soil's water-holding capacity, at intervals of three days until the end of the experimental period in late September. This methodology allowed for a comprehensive assessment of how cadmium exposure affected the growth and physiological responses of both male and female clones.
Results: The results indicated a clear trend: as cadmium concentration increased, both leaf area and height growth of the seedlings decreased significantly. In the control group (0 mg/kg Cd), the highest height growth was recorded at 30.4 cm, while the maximum leaf area recorded was 51.8 cm². Interestingly, the highest total biomass of seedlings (59.2 g) was observed at the 50 mg/kg Cd concentration, suggesting that moderate levels of cadmium might not be as detrimental as higher concentrations. When comparing male and female clones, several key differences emerged. Regardless of the cadmium concentration, male seedlings demonstrated greater growth metrics than their female counterparts. Specifically, the collar diameter growth averaged 2.1 mm for males compared to 2.0 mm for females. In terms of height growth, males reached an average of 21.5 cm, while females achieved 19.9 cm. The leaf area measurements also favored males, with averages of 43.08 cm² for males and 43.64 cm² for females. Total seedling mass showed similar trends, with males averaging 46.48 g and females 44.19 g. Water use efficiency was also higher in males, measuring 0.31 μmol mmol⁻¹ compared to 0.26 μmol mmol⁻¹ in females. Mesophilic conductance and stomatal conductance followed this pattern, with males recording 0.003 mol m⁻² s⁻¹ and 0.45 mol m⁻² s⁻¹, respectively, while females recorded 0.002 mol m⁻² s⁻¹ and 0.39 mol m⁻² s⁻¹. Notably, the only physiological parameter where females outperformed males was in transpiration, with females showing an average of 4.01 mol m⁻² s⁻¹ compared to 3.31 mol m⁻² s⁻¹ in males. Despite the adverse effects of increasing cadmium concentrations on most physiological and growth characteristics—including photosynthesis, water potential, water use efficiency, collar diameter, height, leaf area, and biomass—both male and female clones managed to maintain some level of physiological and growth activity even under high cadmium stress.
Conclusion: In conclusion, both male and female clones of black poplar exhibit a degree of tolerance to high concentrations of cadmium. However, for afforestation projects aimed at rehabilitating Cd-contaminated soils, the male clone (62-167) appears to be more successful than the female clone (62-149). This study highlights the potential for using male black poplar individuals in environmental remediation efforts, emphasizing the importance of selecting appropriate clones based on their physiological responses to pollutants. Future research should focus on elucidating the mechanisms behind cadmium tolerance in these clones, as well as exploring additional strategies for enhancing the resilience of plant species in contaminated environments.