| The intensive exploitation of coal resources is one of the main causes of heavy metal contamination of soils.Gangue dumps are of wide concern as major sites for heavy metal deposition.Coal mining areas have practical requirements for the re-greening of gangue dumps.Compared to physical and chemical soil remediation methods,phytoremediation has the unique advantages of low cost and high public acceptance.However,phytoremediation has long lead times,low efficiency,and is difficult to scale up.This thesis is based on the study of solid composted food waste products,compost-derived dissolved organic matter（DOM）,and compost-derived humic acid（HA）.Exploring the ability and effectiveness of compost products to enhance the transformation of cadmium forms.Study the effects of compost,DOM and HA on the effectiveness of ryegrass in remediating cadmium-contaminated soil and elucidate their mechanism of action.To achieve a rational and scientific use of the resource-based products of kitchen compost and the synergistic and efficient remediation of soil cadmium in gangue dumps.The main conclusions are as follows:（1）Compost,HA,and DOM have different effects on the form of cadmium present in the soil.The main forms of cadmium in soil are weak acid soluble form and reducible form,while the content of cadmium in the residual form,water soluble form,and oxidizable form is less.The addition of compost and HA will result in a decrease in the cadmium of the weak acid soluble form and an increase in the cadmium of the reducible form in the soil.As the proportion of compost and HA applied increased from 5%to 20%,the reducible form increased from16.67～26.68%and 24.21～34.94%to 59.40～70.33%and 37.86～53.06%,respectively.The weak acid soluble form decreased from 80.55～69.05%and 61.65～74.60%to 24.65～37.72%and 42.53～59.35%,respectively.The addition of DOM leads to the conversion of cadmium from the reducible form to the weak acid soluble form and its activation capacity is 5%treatment group>10%treatment group>20%treatment group.（2）The addition of compost,DOM,and HA alters the nutrient content and bacterial community composition of the soil,enhancing the effectiveness of ryegrass in remediating Cd contaminated soil.The addition of compost,DOM,and HA at 20%increased the average soil organic matter content by 23.05,2.32,and 1.00 times,respectively,and the available phosphorus content by 14.67,1.91,and 0.54 times,respectively.Meanwhile,the available potassium and hydrolysable nitrogen content were also increased to some extent.The effect of each treatment group on soil organic matter,available phosphorus,available potassium,and hydrolysable nitrogen at the same application rate was in the order of compost>DOM>HA.The solid phase component plays an important role in the improvement of soil properties.The addition of compost,DOM,and HA reduced the species richness and diversity of the original soil bacterial community,resulting in a change in the structure of the bacterial community.The bacterial community structure was somewhat similar when compost,DOM,and HA were applied at 10%and 20%,but differed somewhat from the 5%treatment group.Proteobacteria,Firmicutes,Actinobacteriota,Chloroflexi,and Acidobacteriota are the dominant phyla under composting,DOM,and HA treatment conditions,accounting for more than 70%of the total bacteria.The addition of compost,DOM,and HA has enabled Cd-resistant bacteria and ryegrass-promoting genera to survive and further evolve into dominant populations in the contaminated soil,such as Bacillus,Lysinibacillus,Pseudomonas,Arthrobacter,Cupriavidus,and Steroidobacter.They play a key role in the transformation of soil Cd forms and Cd remediation by ryegrass.The height of ryegrass plants increased by 1.21～10.44 cm and 0.54～7.47 cm at 5%and10%compost application compared to no compost,respectively,and high application levels inhibited the growth of ryegrass.The ryegrass plant height and above-ground part biomass were optimal at 5%DOM application.The average ryegrass plant height,fresh weight,and dry weight of above-ground parts reached 17.01 cm,1.18 g/10 plants,and 0.16 g/10 plants respectively.HA also increased ryegrass plant height and above-ground biomass,with the greatest increase at a20%application rate.The average plant height,fresh weight,and dry weight of ryegrass can reach 14.41 cm,1.06 g/10 plants,and 0.14 g/10 plants respectively.In addition,DOM and HA promoted the uptake of Cd in ryegrass.Cd accumulation in the above-ground part of ryegrass was increased by 1.82～10.51 and 0.69～1.12 times,and in the below-ground part by 1.26～36.32 and 1.28～3.06 times,respectively,when DOM and HA were applied at 20%.（3）Application of compost improves the ability of ryegrass to remediate cadmium-contaminated soil on gangue sites.The results of the field experiment showed that the addition of 0.625 t.hm-2compost significantly promoted the growth and biomass accumulation of ryegrass.Application of compost could increase the height and root length of ryegrass by 89.55%and 33.33%,the fresh weight of above-ground and below-ground parts by4.70 and 5.42 times,and the dry weight by 2.89 and 1.74 times,respectively.It also increased the cadmium content of the above and below-ground parts of ryegrass by 50.85%and 39.96%,respectively.The bioconcentration factor increased by 73.18%and 60.68%respectively. |
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