| Phytoremediation is an environmentally friendly green technique for solving the problem of heavy metal pollution. Willow and cattail plants are sutiable for phyremediation for their characeteristics of high tolerance to heavy metals, fast growth and rapid regeneration, and large biomass. Adsorption has been studied and applied worldwide for its good cost-efficiency, simple operation and suitability for treatment of low-concentration heavy metals; much attention has been paid to adsorption of heavy metals on agricultural and forest waste for its low cost. The application of biomass of both plants is now onefold, so research on the uptake and adsorption of heavy metals by both plants can develop their new environmental use and is quite significant for the deepening of phytoremediation mechanism and full application of resources.In this paper, the effect of exogenous spermidine (Spd) on the uptake, accumulation, distribution, chemical form, and detoxification of Cd, and the antioxidative mechanism in Salix matsudana and Typha angustifolia in hydroponic solution were studied with Atom Adsorption Spectrometry and Microplate Reader; the adsorption capacity and mechanism of Cd and Pb in solution on cattail AC and willow AC prepared with phosphoric acid activation were investigated by batch experiments.(1) The decrease in biomass of S. matsudana and T. angustifolia induced by Cd was inhibited and the tolerance of both plants to Cd was enhanced by exogenous Spd. Spd increased the accumulation of Cd in root, old cutting of S. matsudana and tissues of T. angustifolia and decreased the content of Cd in twig and leaf of S. matsudana. The concentration of Cd in S. matsudana was in the order root> leaf> twig and was 2002.67-3961 mg/kg,111.59-229.72 mg/kg, and 102.56-221.27 mg/kg, respectively; the concentration of Cd in T. angustifolia was in the order root> rhizome> leaf and was 766.31-1146.52 mg/kg,116.45～204.45 mg/kg,55.54～75.16 mg/kg, respectively.(2) The concentration of Cd in subcelluar of S. matsudana and tissues of T. angustifolia followed the order cell wall> cytosolic fraction> cell organelle。The proportion of Cd in cell wall, cytosolic fraction, and cell organelle respectively in root was 58.73～62.79%,25.02～28.72%, and 7.41～21.21%; in twig was 62.14～64.63%,22.08～26.69%, and 11.57～13.30%; in leaf was 25.11～43.94%, 24.78～28.37%, and 12.38～15.10%. While in T. angustifolia, the proportion of Cd in cell wall, cytosolic fraction, and cell organelle respectively in root was 61.27～63.30%,28.11～29.42%,7.68～10.32%; in rhizome was 52.59～59.52%, 28.59～33.59%, and 11.90～13.83%; in leaf was 63.02～67.94%,25.05～30.58%, and 2.09～9.31%, indicating that the cell wall is the fist detoxification site in the subcell of S. matsudana and T. angustifolia and cytosolic ranks next. In S. matsudana, the greatest amount of Cd of 46.97～60.43% was found in the extraction of NaCl, followed by deionized water and HAC; in T. angustifolia,45.36～66.98% of Cd was in exctraction of NaCl and 15.88～34.88% of Cd involved in HAC extraction, Cd extracted in C2H5OH and deioned water ranked next. The application of Spd decreased the proportion of Cd in extraction solution of C2H5OH and NaCl, but the proportion of Cd in deioned water increased in S. matsudana, contrastly, the effect of exogenous Spd on the proportion of Cd in extraction of NaCl and deioned water was opposite to that in S. matsudana. The results show that exogenous Spd can enhance the tolerance of S. matsudana and T. angustifolia to Cd by declining the level of organic Cd in both plants, promoting the chelation of Cd and inorganic acid in vacuold in S. matsudana and the conbination of Cd with pectic layer and proten containing sulphydryl.(3) The accumulation of superoxide anion (O2·-), hydrogen peroxide (H2O2), and malondialdehyde (MDA) in leaf of S. matsudana increased with the increase of Cd concentration in solution, but decreased by the application of Spd. The activities of superoxide dismutase (SOD), glutathione reductase (GR), and glutathione peroxidase (GPX) and the content of reduced ascorbate (ASA), endogenous Spd, and soluble proten in leaf was decreased by Cd but alleviated by exogenous Spd. Cd induced the increase of Put and nitric oxide (NO) in a dose-effect way, exogenous Spd inhibited the increase of Put, but promoted the increase of NO. The analysis of correlation indicates that exogenous Spd could enhance the tolerance of S. matsudana to Cd through elevating the activities of SOD and GPX, especiall that of CAT, APX, and GR, and the concentrations of reduced glutathione (GSH) and ASA; corespondingly catalase (CAT), ascorbate peroxidase (APX), GSH, NO, and soluble protein, especially putrescine (Put), probably act as signal molecule to induce the initiation of other antioxidative mechanism and indirectly alleviate the oxidative damage of Cd on S. matsudana. The content of Cu and Zn in root and leaf of S. matsudana was declined by Cd treatment in a dose-effect pattern and enhanced by exogenous Spd, however the effect of Spd on Zn content in root and leaf was different. The accumulation of Fe was inhibited by Cd treatment; lowered the Fe content in root and leaf was lowered after Spd appilication under low content Cd treatment but elevated in high Cd content solution. The values of translocation factor (TF) of Zn was decreased by Cd but elevated by exogenous Spd; while the translocation capacity of Fe was enhanced both by Cd and Spd.(4) Cattail activated carbon (AC) has an unequal cylinder with a rough suface and the surface of cattail AC is rough with a layer structure. Willow AC mainly contain mid-and micropore and function groups of O-H, C=O, C-O, and P=O, the BET surface area and pHIEp of cattail AC and willow AC is 130.42 m2/g and 234.42 m2/g,3.4 and 4.3, respectively. The adsorption of Cd and Pb on cattail AC and willow AC was rapid and the time for adsorption was 10 min or so; the adsorption capacity of Cd and Pb increased with the increase of initial pH valus, temperature of solution, but decreased with the application of both AC. The pseudo second-order sorption model, both Langmuirand Freundlich models fitted the adsorption data and process very well. Equilibrium adsorption data of both metal ions fitted reasonably well with; the maximum sorption capacity Qm of Cd and Pb on cattail AC and willow AC obtained from Langmuir isotherm was found to be 40.98 and 58.82 mg/g and 48.08 and 61.73 mg/g, respectively, at the pH value of 5 and temperature of 25 ℃; the adsorption process was spontaneous and endothermic, moreover, the spontaneity and feasibility increased with temperature and the Pb sorption was more spontaneous than that of Cd. The adsorption of Cd and Pb on both AC involved physico-chemical reactions. The film diffusion and intraparticle diffusion occurred simultaneous and the intraparticle diffusion and chemical adsorption both were the rate limitted steps of adsorption.(5) The tolerance of S. matsudana to Cd is high than thas of T. angustifolia and the uptake capacity of Cd calculated according to the biomass in S. matsudana was bigger than that of T. angustifolia; compared to willow AC, the isoelectrical point (pHIRP) of cattail AC was lower, the area of adsorption peak was bigger and lower before and after adsorption, respectively, suggesting much more function groups of cattail AC involved in the chemical sorption of Cd and Pb, but the physical characteristics of willow AC was better than that of cattail AC; the adsorption of Cd and Pb on cattail AC was larger in the lower initial pH solution and more suitable to temperature of solution; the adsorption of Cd and Pb on cattail AC was faster, more spontaneous, lower energy need, better order, and high capacity compared with willow AC. |
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