Effects And Mechanism Of Fulvic Acid On The Two Submerged Plants Under Lead Stress

Lead, As one of the “Five poisons” heavy metals, brought a serious threat to aquatic plants, animals, and human health after entering to the water. Phytoremediation technology in the application of water heavy metal pollution greatly alleviated the lead contamination problem. Fulvic acid(FA), as a kind of natural organic acid in nature, can effectively alleviate the lead stress in the plants. The study taking two submerged plants(Vallisneria and Potamogeton crispus L.) as the research object, researched the ameliorating effects mechanism of fulvic acid on heavy metal lead stress on the plants. The results are as follows:With the increase of lead concentrations and the extension of time, the chlorophyll contents of Vallisneria and Potamogeton crispus L. increased firstly then decreased, the MDA content of Vallisneria continuously increased, at the 250 μmol·L-1 lead concentration, the MDA content of Vallisneria reduced at the end of lead stress; the MDA content of Potamogeton crispus L. increased firstly then decreased. The Fpro content of Vallisneria increased firstly and decreased at the end; The Fpro content of Potamogeton crispus L.kept reducing.The activity of SOD, CAT and POD in these two plants increased firstly and decreased at the end with the increase of lead concentrations and the extension of time.Their CAT activities were the most sensitive under lead stress; at high lead concentrations, three kinds of antioxidant enzymes in two plants were inhibited and reduced rapidly, but they were lower than the blank group. Under the high concentrations of lead stress, Potamogeton crispus L.showed better resistance.Under the lead stress, the activity of NR, GS and ACP in Vallisneria and Potamogeton crispus L. presented a trend of promotion in low concentration and inhibition in high concentration. At high lead concentration, The activity of NR, GS and ACP in Potamogeton crispus L.was lower than blank group and more Sensitive than that in Vallisneria. With the extension of time, The activity of NR, GS and ACP in these two plants increased firstly then decreased, they all were the lowest on the seventh day.After adding the FA solution into nutrient solution, at the 50 μmol·L-1 lead concentration, the chlorophyll content of Vallisneria gradually increased firstly then decreased as long as the content of FA increasing, but the MDA decreased firstly then increased; the chlorophyll content of Potamogeton crispus L.decreased firstly then increased as long as the content of FA increasing, but the MDA content decreased slowly. At the 50 μmol·L-1 lead concentration, the chlorophyll content of two submerged plants increased firstly then decreased, but they all were higher than bland group; The change trend of MDA content in two plants was in accordance with that of chlorophyll content.At low lead concentration, with the increase of lead concentrations, the activity of SOD in Vallisneria and Potamogeton crispus L. increased firstly then decreased and was significantly lower than blank group(p<0.05), the activity of SOD in Vallisneria also was lower than FA0 control group;the activity of CAT in Vallisneria and Potamogeton crispus L. showed no difference with that of SOD; their activity of POD kept decreasing. At high lead concentration, the change of the activity of SOD and CAT in Vallisneria and Potamogeton crispus L. showed no difference with that at low lead concentration, their activity of CAT was higher than blank group, the activity of POD in Vallisneria gradually reduced, the activity of POD in Potamogeton crispus L.increased firstly then decreased. At high lead concentration, The ameliorating effects of FA showed the best in the activity of CAT.At the 50 μmol·L-1 lead concentration, the activity of NR in Vallisneria decreased firstly then increased; that of GS and ACP in Vallisneria Continully increased with the increase of lead concentrations, the activity of GS and ACP was significantly higher than blank group(p<0.05), the activity of NR and GS in Potamogeton crispus L.was increased firstly then decreased and higher than blank group(p<0.05), its activity of ACP increased firstly then decreased. At the 100 μmol·L-1 lead concentration, the activity of NR in Vallisneria and Potamogeton crispus L.increased firstly then decreased as long as the content of FA increasing, and was higher than blank group, the activity of GS in Vallisneria increased, that in Potamogeton crispus L.had no difference with the activity of NR, their activity of ACP increased firstly then decreased. No matter at low or high concentration lead stress, FA effectively improved the activity of NR, GS and ACP in Vallisneria and Potamogeton crispus L..The addition of FA could significantly reduce the amount of lead innutrient solution. The chelate reaction between FA and Pb could form a morphology which is easily to be absorbed by the plants, then the Pb uptake ability of plants was inproved. FA increased Pb translocation from roots to the ground part(leaves) and improved the accumulation of lead in plants. FA couldn’t change Pb various chemical forms in plant roots and leaves, but could change its percentage. The first three main chemical forms of extractable Pb in Vallisneria and Potamogeton crispus L.were FHAc,FE and FW, FNa Cl and FHCl were second, FR was last.