| Pentachloronitrobenzene (PCNB) is a fungicide belonging to the organochlorine family, extensively for crop production and become an environmental concern. It seriously affects the quality of agricultural products and likely becomes hazardous to human health. The aim of the study was to comparatively analyze six different cultivars of alfalfa to accumulate and degrade PCNB from the contaminated soil and evaluate the potential phytoremediation of the soil. Therefore, six alfalfa cultivars, namely, Zhong Mul, Gold Empress, Gannong 3, WL323, WL232 and Longdong, were used as the test plant to grown in the soils spiked with 10 mg kg"1 PCNB to assess their potential for the degradation of PCNB, along with the accumulation of PCNB and biological parameters. Finally, the activities of urease (URE), invertase (INV), polyphenol oxidase (PPO), acid phosphatase (ACP) and alkaline phosphatase (ALP) were assayed in the polluted soil and restored soils to indicative of changes in soil health.Alfalfa cultivars were grown in soil with PCNB to investigate its residues in the soil and several PCNB-induced stress responses. The alfalfa cultivars varied widely in their ability to accumulate and translocate PCNB. The degradation by plants came up to 66.26-77.68% of the total amount of PCNB spiked in the soil, while that was only 48.42% in the control (soil without alfalfa) after a 20 d experiment. The lowest degradation of PCNB was Gold Empress, while the highest was Longdong 3, indicating the ability of removal of PCNB was varied considerably. The alfalfa species can absorb and accumulate PCNB. The PCNB accumulated by the shoot varied from 1.304μg g-1 FW to 2.317μg g-1 FW, while the PCNB in the roots ranged from 8.603 μg g-1 FW to 36.244 μg g-1 FW. The data indicated that capability of accumulation varied considerably and the concentrations of PCNB in shoots were considerably lower than that in roots. Besides, the phytoextraction of the PCNB only account little percentage of the total PCNB, varying from 0.33% to 0.83% and the biodegradation ranged from 17.51% to 28.42%. This suggested the PCNB in the soil was degraded by plants based on the biodegradation. Moreover, concentrations of PCNB residues in rhizosphere were significantly higher than those in non-rhizosphere soils.To investigate the effect of PCNB on biological parameters, several physiological responses were determined. Further analysis revealed that alfalfa exposed to 10 mg kg-1 PCNB showed growth stunt and oxidative damage. The chlorophlly content of Gannong 3 was inhibited significantly and the concentration of TBARS in leaves of Gannong 3 was increased significantly. The concentration of TBARS in roots except the Gold Empress and WL323 were decreased significantly. Besides, all the species increased the abundance of O2- and H2O2. Above all, the cultivars differed considerably, indicating that the alfalfa cultivars have different tolerance to PCNB.Finally, activities of invertase (INV), urease (URE), polyphenol oxidase (PPO), alkaline phosphatase (ALP) and acid phosphatase (ACP) were assayed in the treated soil. Activities of the enzymes were altered after PCNB exposure. Interestingly, the URE, PPO, ALP and ACP activities were increased in soil following the planting of alfalfa. The present study allowed us to screen some desirable alfalfa cultivars that meet the requirement used for degradation of PCNB. |
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