Effects Of Manganese On The Ecotoxicological Response And Nitrogen Metabolism In Hyperaccumulators Polygonum Pubescens Blume And Polygonum Hydropiper L.

At present, metal-polluted soils is one of the most important concerns for scientists, explore effective method actively of remediating metal-polluted soils has become a hotspot. Phytoremediation gained highly attention due to its low cost, friendly to environment without destroying the soil physical and chemical properties. Polygonum pubescens Blume was new Mn hyperaccumulator which discovered in China. It is much better material for remediating Mn-polluted soils. Hydroponic culture were conducted in this study to investigate the effects of Mn as well as Mn-Zn on the eco-toxicological response and nitrogen metabolism in hyperaccumulating plants Polygonum pubescens Blume and Polygonum hydropiper L.. Research findings were as follows:1. The plant height and weight of P. pubescens were no significantly affected when exposed to single Mn concentration lower than 1 mmol L-1 (p> 0.05), but significant changes were found for P. hydropiper (p< 0.05), compared with those of the control ones. At the same time, the chlorophyll contents in both plants significantly (p< 0.05) decreased when exposed to Mn. The height and weight of P. pubescens as well as the weight of P. hydropiper were significantly decreased under the combined contaminations of Mn and Zn. The height and weight of P. pubescens were significantly decreased by 78 and 56%, respectively, when exposed to 100 mg·L-1 Mn and 100 mg·L-1 Zn. The variation tendency of chlorophyll contents were similar to biomass.2. The Mn contents increased significantly (p< 0.05) in the tissues of both plants with the increased concentrations of single Mn treatment. However, the Mn levels in P. pubescens were always higher than those in the same tissues in P. hydropiper when under the same single Mn treatment, indicating that the P. pubescens is more Mn-tolerant. Mn contents in both plants leaves decreased by Zn when exposed to 0,10,100 mg·L-1 Mn. It showed that Mn contents in P. pubescens leaves were inhibited by Zn. On the contrary, Zn contents in both plants leaves increased by Mn when exposed to 0 and 10 mg·L-1 Mn combined with different Zn level, indicating that Mn is favor of Zn absorbed in both plant.3. The contents of MDA and H2O2 in Polygonum pubescens and Polygonum hydropiper were different when under single Mn as well as Mn-Zn. The contents of H2O2 and MDA in both plants were significantly increased when expose to 4 and 8 mmol·L-1 Mn (p< 0.05) compared to the control. However, the MDA contents in P. pubescens leaves and roots as well as in P(?) hydropipe leaves were significantly increased (p< 0.05), but the opposite was found for P(?) hydropipe roots. It showed that the lipid peroxidation degree can be aggravated when exposed to the combined contamination of Mn and Zn.4. Enzymatic antioxidants and non-enzymatic antioxidants are play an important role in resist Mn.The SOD activities in P. pubescens leaves increased by 1.33,1.40 and 1.48 times compared to the control, respectively, when exposed to 2～8 mmol·L-1 Mn while the SOD activities decreased in roots of two plants. The activities of enzymatic antioxidant (POD, CAT and APX) increased below 2 mmol.L-1 Mn treatment and then decreased in the leaves and roots of P. pubescens Blume and P. hydropipe. The activities of POD, CAT and APX were 1.89 1.37 and 1.74 times respectively compared with those of the control. The contents of GSH and -SH in both two plants were increased significantly under the treatment of 8 mmol·L-1 Mn, the -SH contents were 1.11 and 1.29 times in P. pubescens leaves and roots, the GSH contents were 1.27 and 1.45 times compared to the control, respectively. However, the concentrations of PCs have not significantly changed (p> 0.05) in P. pubescens and P. hydropipe leaves. It indicates that the-SH and GSH play an important part in detoxicating metals.5. The contents of nitrate nitrogen in P. pubescens decreased significantly (p< 0.05) while the contents of soluble protein increased at Mn treatment alone. The contents of nitrate nitrogen and ammonium nitrogen in P. hydropiper leaves were increased sharply by 1.89 and 1.76 times in the treatment of 8 mmol L-1 Mn, and the solube protein contents in the leaves and roots of P, pubescens reached the highest values by 2.68 and 1.25 time under 2 mmol L-1 Mn, respectively, compared to the control. The contents of free proline in P. hydropiper leaves and roots were significantly increased (p< 0.05). When exposed to the combined contaminations of 100 mg·L-1 Mn and 100 mg·L-1 Zn, the contents of NO3- in the roots of both plants were declined and NH4+ contents in the leaves of P. pubescens also decreased. Besides, the contents of free proline and soluble protein increased in P. pubescens roots. It showed that the free proline played an important part in detoxcating NH4+6. The key nitrogen metabolism enzymes in both plants changed when exposed in single Mn. Both activities of NR in P. hydropiper leaves and GS in P. pubescens leaves were declined significantly (p< 0.05) at single Mn treatment. The activities of GOGAT in both plant tissues decreased significantly (p< 0.05) with the Mn concentrations from 2 to 8 mmol L-1, compared with those of the control ones. In addition to these, the GDH activities in both plant leaves (p< 0.05) rose under single Mn treatment, the GDH activities in P. pubescens leaves were 5.06,10.43, 13.44 and 16.29 times compared to the control, respectively. The GDH activities in P. hydropiper leaves reached the highest value, was 3.07 times to control. The activities of NR, GS, GOGAT in P. pubescens leaves increased significantly (p< 0.05) when exposed to the different Mn treatments added with 100 mg·L-1 Zn. Meanwhile, the activities of GDH in both plants changed along with the different combined contents of Mn and Zn. Compare to the control, the GDH activities in P. pubescens leaves and roots were stimulated by 1.57 and 1.88 times respectively, when exposed to 100 mg·L-1 Mn treatments added with 100 mg·L-1 Zn while the GDH activities in P. hydropiper leaves and roots were significantly inhibited (p< 0.05) by 0.59 and 0.20 times, respectively.