| Cadmium(Cd)is one of the most toxic heavy metal elements.Cadmium pollution in farmland soil will not only lead to the deterioration of soil environmental quality,but also affect the normal growth and development of plants and reduce the yield and quality of crops.Cadmium enters human body through the food chain,causing great harm to human life,health,and farmland soil ecosystems.Therefore,it is of great significance to study the remediation of Cd-contaminated soil in farmland.Compared with other hyperaccumulators,cotton,as a cash crop,has the characteristics of large biomass,strong environmental adaptability,non-edible,and strong absorption and enrichment ability of heavy metal ions.In this paper,pot experiments were conducted to investigate the effects of Cd pollution on the growth and development of cotton plants,as well as the absorption,transportation and enrichment of Cd by cotton.And also studied the enhanced remediation of Cd pollution in soil by combining exogenous melatonin(MT)and tetrasodium glutamate diacetate(GLDA)on cotton plants.Melatonin is a kind of plant hormone,and GLDA is a new green degradable chelating agent.Through the above research on strengthening the remediation of Cd pollution in soil,it is hoped to provide reference for the enhanced remediation technology of Cd pollution in farmland soil.The main results of the study are as follows:(1)Exogenous MT of 50 μmol/L could significantly improved the Cd tolerance of cotton seedlings and alleviate Cd toxicity.The growth and development of cotton plants were significantly inhibited by 300 μmol/L Cd stress,but which can be effectively alleviated by adding exogenous MT.And the different degrees of alleviating Cd stress in cotton seedlings were obtained by different MT treatment concentrations.The effect on alleviating Cd stress in seedlings was not significant at the low concentration MT treatment(10 μmol/L,M1),while the stress effect on plants could be aggravated at the high concentration MT treatment(100 μmol/L,M3)to some extent.However,compared with Cdmium stress alone,the growth of cotton seedlings was the most vigorous under50 μmol/L MT treatment,and the contents of chlorophyll a(chla),chlorophyll b(chlb)and total chlorophyll in leaves were increased by 52.11%,54.95% and 52.90%,respectively.Net photosynthetic rate(A),transpiration rate(E),stomatal conductance(Gs)and intercellular carbon dioxide concentration(Ci)were increased by 18.37%,19.34%,32.35% and 5.10%,respectively.The superoxide dismutase(SOD)activities were significantly increased under the three MT concentrations,but there was no significant difference among different MT concentrations.The activity of peroxidase(POD)was significantly increased under 10 μmol/L MT treatment and 50 μmol/L MT treatment.The activity of catalase(CAT),glutathione reductase(GR)and ascorbate peroxidase(APX)significantly increased by 175.59%,17.86% and 3.98% at 50 μmol/L MT,respectively.The contents of malondialdehyde(MDA),soluble sugar,free proline,and electrical conductivity were significantly decreased 22.64%,36.82%,11.58% and 18.05% at 50μmol/L MT,respectively.While the content of soluble protein increased by 31.84%.The results showed that exogenous MT could alleviate the oxidative stress caused by Cd toxicity,enhance the photosynthetic pigment content and photosynthetic efficiency of cotton seedlings,improve the activity of antioxidant enzymes,regulate the content of osmotic regulatory substances,and improve the stress resistance of cotton seedlings,and alleviate Cd toxicity.Among them,M2(50 μmol/L)had the best effect.(2)The effect on Cd stress on the growth of cotton seedlings can be effectively alleviated by the combination of GLDA and MT(50 μmol/L MT+10 mmol/L GLDA).The enhanced remediation of Cd pollution by cotton plants in farmland soil was conducted with a combination of M2(50 μmol/L)and different concentrations of GLDA(G1: 2.5mmol/L;G2: 5mmol/L;G3: 10 mmol/L).The results showed that the combined treatment of G3M2 reduced the Cd content in the roots of cotton plants,improved their tolerance to Cd stress,and resulted in the best growth of cotton seedlings.Compared with Cd treatment alone,chlorophyll content increased by 39.86%,and photosynthetic efficiency increased by 22.29%.The activities of SOD,POD,CAT,GR and APX were increased by 18.42%,56.77%,167.72%,9.97% and 14.58%,respectively.The content of MDA,soluble sugar,free proline,and electrical conductivity of leaves decreased by42.62%,25.98%,8.09% and 24.77%,respectively.(3)The combined treatment of MT and GLDA(50 μmol/L MT+10 mmol/L GLDA)enhanced the absorption,transport and enrichment of Cd in cotton plants,and improved the remediation effect of cotton on the Cd pollution soil.The results were as follows:(1)The contents of Cd in all organs of plants was significantly increased under Cd treatment,especially in the roots,reaching 22.02 mg/kg,which was 15.44 times higher than that in control(CK)at 1.34 mg/kg.The addition of exogenous MT significantly reduced the Cd content in the roots,leaves and petioles,and seeds.The application of GLDA significantly increased the Cd content in above-ground parts of plants,especially the Cd content in leaves,which increased by 43.23% compared to Cd treatment alone.The combined treatment of GLDA and MT significantly increased the Cd content in the aboveground parts of cotton plants,which was 31.04% higher than that of GLDA treatment alone.Therefore,the combined treatment of GLDA and MT significantly enhanced the absorption of Cd in the aboveground parts of cotton plants(2)Cadmium treatment significantly reduced the transport and enrichment of Cd in plants,while exogenous MT treatment significantly increased the transport coefficient of Cd in plants,which increased by 54.84% compared to Cd treatment alone.However,there was no significant difference in the impact on the enrichment coefficient compared to Cd treatment alone.GLDA significantly improved the transport and enrichment coefficients of cotton plants,with increases of 64.52% and 27.50% compared to cadmium treatment alone.The transport coefficient and enrichment coefficient of cotton plants under the combined treatment of GLDA and MT increased by 111.29% and 92.50% compared to Cd treatment alone.According to the study,it was found that the combination of 50 μmol/L MT and 10mmol/L GLDA could not only alleviate the cadmium toxicity of cotton and improve the resistance of plants to cadmium,but also enhance the accumulation of cadmium in cotton plants,so as to repair the soil cadmium pollution. |
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