Analysis Of The Remediation Mechanism And Effect Of Rhizosphere Soil Using Bacterial Manure Fertilizer In Lead & Zinc Mining Polluted Area

The studied area, Zixing Pb/Zn mining rigion, Hunan province, is not only severely co-contaminated by Pb, Zn, and Cd but also poor in soil properties and low in mineral nutrients. High content of lead and zinc in the soil prevents the survival of most microbes and plants in this environment. Moreover, Pb/Zn mining polluted soils usually have a poor water-holding capacity which can lead further threat to plant growth and survival during the dry season. Therefore, the key measure to cultivate plants on heavy metal contaminated soil is to improve the rhizosphere condition. In this study, a new kind of bio-organic manure with high water-retention potential specifically made-up for reducing the metal toxicity was applied as base fertilizer to improve the root growth environment. The manure contains a heavy metal-resistent strain, Aspergillus oryzae HA, isolated from mining waste and incubated under high Pb/Zn concentration conditions. The fungus HA was used to alleviate the heavy metal toxic effect in the rhizosphere and enhance the fertilizer efficiency. The main objective of this study is to analyze the remediation mechanism and effect of the applied bacterial manure based on pot trials and field ecological remediation engineering experiment. The main findings are as follows:(1) Pot trials:Pot trials were carried out to investigate the effectiveness of the kind of bio-organic fertilizer to promote the survival, growth and heavy metals uptake and accumulation in chili(Capsicum annuu), sunflower(Helianthus annuus), tomato(Lycopersicon esculentum) and peanut(Arachis hypogaea) under site soils collected from local tailing of lead-zinc deposit.① Plant survival rate:The bio-organic fertilizer improved the survival rate of these four plants. In control group, tomatoes and sunflowers were not survival, peppers and peanuts were survival, but with a short height, yellow leaves, and thin stems, obviously. While in bio-organic fertilizer treatments, four kinds of plants were all survival, and with high quality.② The plant growth condition were as follows:In control group, plants grew slowly, with low biomass and short height and even died, while the plant survival rate, biomass and height were improved obviously in bio-organic fertilizer treatments. Further, chili and sunflower in bio-organic fertilizer treatments bear fruits respectively while in CK treatments they did not produce fruits at all. Little differencees were showed in different plant species for both plant height and biomass, showing a trend Control group< potassium fertilizer< NPK compound fertilizer< bio-organic fertilizer. Compared to the control alone, bio-organic fertilizer significantly enhanced plant height of 55.1%,102.0%,37.0% and 79.1% and dry biomass of 456.6%, 363.6%,224.7% and 770.0% for chili, tomato, peanut and sunflower, respectively.③ The uptake and accumulation characteristics of heavy metals in plants:the use of the bio-organic fertilizer:a) led to a significant reduction of heavy metal concentration in above-ground parts of plants alleviating the toxicity of heavy metals to shoots, thus promoting plant growth, indicating that bio-organic fertilizer treatments are capable of reducing ecological risk to soil-inhabiting plants exposed to heavy metals; b) promoted root growth, both in biomass and the amount of fibrous root,and increased the heavy metal concentration in root, equivalent to enhance root resistance and therefor root activity increased correspondingly; c) the amount of heavy metals in the above-and under-ground increased significantly indicating a promotion on transport upwards and animmobilization in roots, respectively which can be effective for phytoextraction.④ Plant rhizospheric microbe:The bio-organic fertilizer significantly promoted microbial communities in the rhizospheric soil, mainly the increase of the total microbial number. Compared to the control, the total microbial number was increased after the bio-organic fertilizer was in and as a result the structure of the microbial communities was changed.(2) And the bio-organic fertilizer was also applied to the ecological restoration demonstration project area in Zixing.① Plant survival rate:Plants survival rate was significantly increased, which showed practical significance for the restoration of heavy metal contaminated soils. The plant survival rate was 85% after the first year. The following year reseeded the plants and the plant survival rate reached 100%.② Plant growth condition:The six kinds of plants were thriving along streams and grew normally. Sweet osmanthus(Osmanthus fragrans) and Bougainvillea Goldraintree(Koelreuteria bipinnata Franch) yielded the highest biomass a year, while Schima(Schima superb Gardn. et Champ) and Chinese yew (Taxus chinensis) produced the lowest biomass a year. Bead tree (Melia azedarach Linn) and Chinese tallow tree(Sapium sebiferum) were the fastest-growing plants among these six plants.③ Plant rhizospheric microbe:The bio-organic fertilizer increased the total microbial number in the rhizospheric soil of six kinds of plants. This result was consistent with the experiment of rhizospheric soil microbial communities for four kinds of plants in pots.The main innovation of this study is proposing a view that the key remediation of heavy metal polluted soils is the improvement of plant rhizosphere environment. And based on the degree of soil pollution and physical and chemical properties, a new kind of bio-organic fertilizer with Aspergillus oryzae HA was made. The results show that the bio-organic organic fertilizer can reduce the toxicity of heavy metals in soil, improve the survival rate of plants, and promote plant growth. That is to say, the bio-organic organic fertilizer can play an important role in the restoration in Pb/Zn Mining area.