| Mercury（Hg）is a persistent,toxic and well-established global contaminant.In the atmosphere,the Hg mainly exists as the gaseous elemental Hg（GEM）,which accounts for more than 95%of total gaseous mercury.The GEM mainly comes from both anthropogenic and natural sources.Although extensive studies have been devoted to estimating anthropogenic Hg emissions,studies on Hg estimation from natural sources are insufficient.Furthermore,soils account for more than90%of Hg stored in terrestrial ecosystems,with global topsoil Hg pools（0-40 cm）estimated as being>300 000 Mg,induced the release of Hg from natural substrates（i.e.,water,vegetables,soils and rocks）are a significant source of GEM,and accounts for up to two-thirds of the global Hg input to the atmosphere.In addition,the GEM is accumulated in closed circumstance of greenhouse,resulted in the leaf Hg was more uptaked the GEM in greenhouse.Generally,the fertilizers are often applied in order to promoted crop growth and improved the quality of agricultural products for greenhouse production.At the same time,fertilizers contain a wealth of organic matter,minerals and cation exchange capacity,which can affect the chemical properties of Hg in soil through chelation,adsorption and oxidation.Based on this conclusion,this study is based on the simulated greenhouse,and unpolluted soil with Hg is the research object,which to investigate the influence of the soil-air Hg（0）release fluxes,the valence states of Hg（Hg（0）,Hg（I）and Hg（II））,the soil total mercury（THg）,the soil properties（SOM,CEC,Eh and pH）and environmental factors（light intensity,soil moisture and temperature）in greenhouse soil after amended with humic acid fertilizer,enzyme and organic fertilizer.Hereby,the mechanism of soil Hg（0）release and valence transformation were analyzed based on the correlation of these indexes.The main conclusions are as follows:（1）In the greenhouse environment,the soil-air Hg（0）release flux of blank soil（CK）showing a decreasing tendency over time,which ranged from and mean were 104.97-42.32(73.01±25.80 ng·（m~2·h）-1),they were much higher than that of agricultural fields(broomcorn of 35.38ng·（m~2·h）-1,corn of 28.76 ng·（m~2·h）-1).The GEM in greenhouse is predominantly come from soil-air Hg（0）release fluxes,and is accumulated in greenhouses,with the ranged from and mean 3.72-102.04（68.75±44.70 ng/m~3）,which is much higher than that of farmland（3.26-10.8 ng/m~3）.After the soil amended with humic acid fertilizer,enzyme and organic fertilizer,the soil-air Hg（0）release fluxes showed a decreasing tendency with the increasing fertilizer dosage,and the mean of soil-air Hg（0）release fluxes respectively were 22.99 ng·（m~2·h）-1（organic fertilizer）>20.51 ng·（m~2·h）-1（humic acid fertilizer）>14.77 ng·（m~2·h）-1（enzyme）,which the mean of GEM respectively were 27.99 ng/m~3（organic fertilizer）>15.83 ng/m~3（humic acid fertilizer）>11.66 ng/m~3（enzyme）,and had best influence effect of the soil-air Hg（0）release fluxe and GEM for applying with enzyme in soil.（2）The oxidation process of soil Hg via Hg（0）/Hg（I）and Hg（I）/Hg（II）can be promoted in greenhouse soil after amended with humic acid fertilizer,enzyme and organic fertilizer,and showing a increasing tendency with the increasing fertilizer dosages,which caused the soil Hg（0）and Hg（I）decreased with the increasing fertilizer dosages.The mean concentration of soil Hg（0）respectively were 0.86 ng/g（CK）>0.48 ng/g（organic fertilizer）>0.43 ng/g（humic acid fertilizer）>0.25ng/g（enzyme）,and the mean concentration of soil Hg（I）respectively were 18.69 ng/g（CK）>13.56 ng/g（organic fertilizer）>9.96 ng/g（humic acid fertilizer）>7.54 ng/g（enzyme）,lead to the soil Hg（0）release was inhibited.In addition,the oxidation process of soil Hg by Hg（0）/Hg（I）and Hg（I）/Hg（II）can be better stimulated with applying the enzyme.The soil Hg（II）and THg increased were increasing with fertilizer dosage due to the Hg carried with the fertilizer（330.87 ng/g（organic fertilizer）>302.34 ng/g（humic acid fertilizer）>263.87 ng/g（enzyme））and the oxidation process of soil Hg was promoted（the mean concentration of soil Hg（II）respectively were 137.03 ng/g（humic acid fertilizer）>124.38ng/g（enzyme）>121.67 ng/g（organic fertilizer）>75.34 ng/g（CK）;the soil THg mean concentration respectively were 147.42 ng/g（humic acid fertilizer）>135.71 ng/g（organic fertilizer）>132.17 ng/g（enzyme）>94.89ng/g（CK））.The correlation analysis indicated that the soil-air Hg（0）release fluxes were mainly from soil Hg（0）release.These result shown that the generation of soil Hg（0）was underwent the reduction process of Hg（II）/Hg（I）and Hg（I）/Hg（0）,but not come from the direct reduction of Hg（II）/Hg（0）.The soil Hg（II）is the main form of soil Hg.（3）During 0-120 d,the light intensity and temperature of all treatments gradually increased,and soil moisture did not significantly variation.For CK,humic acid fertilizer,enzyme and organic fertilizer treatments group,the soil propertie mean contents were SOM:66.79 g/kg（enzyme）>0.90 g/kg（humic acid fertilizer）>55.87 g/kg（organic fertilizer）>49.39 g/kg（CK）;Eh:622.04 m V（enzyme）>622.00 m V（humic acid fertilizer）>621.54 m V（organic fertilizer）>607.00 m V（CK）;PH:6.70（enzyme）>6.45（CK）>6.13（organic fertilizer）>6.04（humic acid fertilizer）;CEC:22.75 cmol/kg（humic acid fertilizer）>19.11 cmol/kg（organic fertilizer）>17.90 cmol/kg（CK）>17.10 cmol/kg（enzyme）,respectively.Applying humic acid and organic fertilizer can be increased soil SOM,soil Eh and soil CEC,and decreased soil pH.During 0-120 d,the soil SOM and CEC did not significantly variation,and soil pH gradually decreased.Moreover,the soil Eh showed a decreasing tendency during the 0-30,then reached the equilibrium on the 60 d amended with humic acid and organic fertilizer.The soil SOM,soil Eh,and soil pH can be enhanced with the enzyme.During 0-120 d,soil SOM and CEC did not significantly variation,and soil pH decreased gradually.On the 0-30 d,the Eh showed a decreasing tendency,then to be enhanced for amended with 1%-enzyme,For 3%and 5%enzyme,the soil showed a increasing tendency during 0-120 d,and reached the equilibrium on the 60 d.（4）The surface of humic acid fertilizer and organic fertilizer are rough and contains more micropores than the CK,which can promote Hg（0）enter the surface of fertilizer or soil from micropores.For CK,humic acid fertilizer（100%-HA）,organic fertilizer（100%-OF）and soil with applying equal proportion of enzyme（100%-enzyme-Hg（0））were involved-COOH,-C-O and-C=O functional groups,which the100%-HA and 100%-OF also contained-OH functional group,Cl and S elements.Furthermore,100%-enzyme-Hg（0）also contained Cl element.The Fourier Transform Infrared Spectrum（FTIR）demonstrated that the Hg（0）was combined with-OH,-COOH,-C-O and-C=O functional groups.Other studies showed that the Cl element can be promoted the oxidation of Hg（0）.Thus the adsorption and oxidation of Hg（0）were enhanced for soil amended humic acid fertilizer,organic fertilizer and enzyme.（5）After the soil amending with humic acid fertilizer,enzyme and organic fertilizer,ambient environment conditions are no longer the key factors,and the soil properties are the dominant factors,involved in the soil-air Hg（0）release process in the greenhouse environment.In general,first,the redox state of soil was controlled by the variation of soil Eh applying the humic acid fertilizer,enzyme and organic fertilizer,which the soil Eh was enhanced after amending with humic acid fertilizer,enzyme and organic fertilizer,resulting in the soil environment was in oxidation state,then the oxidation process of Hg（0）through Hg（0）/Hg（I）and Hg（I）/Hg（II）were promoted,leading to the release of soil Hg（0）was inhibited,and the soil-air Hg（0）release fluxes was reduced.Subsequently,the activity and reducibility of soil Hg were influenced according the variation of other soil properties to be influenced the transformation of the soil Hg valence states（Hg（0）,Hg（I）and Hg（II））amending with humic acid fertilizer,enzyme and organic fertilizer,which the soil-air Hg（0）release fluxes were impacted. |
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