关键词: 离子型稀土矿尾砂, 植被生态修复, 农林废弃物, 土壤养分, 土壤微生物

Abstract:

Owing to long-term unordered mining in ionic rare earth mining areas, the habitats of plants and animals have been damaged and fragmented, resulting in severely degraded biodiversity. In addition, mining and stripping of topsoil cause soil erosion, leading to nutrient loss and accelerating soil impoverishment. Therefore, natural restoration of ecosystems has become difficult, and the restoration process of mining-area ecosystems has long been without human-assisted intervention in ecological restoration. In the past, ecological restoration was mainly performed using the guest-soil method; however, the restoration costs were too high and difficult to promote. The use of organic materials from agricultural and forestry waste resources to improve the soil matrix of ionic rare-earth tailings has become increasingly popular owing to their low cost and high efficiency. To study the ecological effects of organic materials on the soil matrix of ionic rare earth mine tailings, the camellia seed shells (abbr. as YCGK from Chinese), and peanut shells (abbr. for HSK), corn straw (abbr. as YMJG), pine nuts (abbr. as SG), and garden plant leaves (abbr. as LY) were selected as test materials to improve the physicochemical properties of rare-earth tailing soil, enhance soil fertility, and promote the restoration of soil microbial diversity. The pot experiments in laboratory were conducted using the individual fertilization experiment methods, with rare earth tailing soil without added any materials as the blank control (CK), and five treatments including 0.15 kg YCGK, 0.15 kg HSK, 0.15 kg YMJG, 0.15 kg SG, and 0.35 kg LY per repeated experiment were applied separately. The soil physicochemical properties of each treatment were analyzed, and the soil bacterial diversity and community structure of each treatment were analyzed using 16S rDNA gene sequencing. The results indicated that the tested material was suitable for improving the soil matrix. The physicochemical properties and nutrition of the soil were improved using the tested materials. The soil pH values of each treatment were significantly higher than those of CK (p<0.05), and the soil pH was adjusted in the following order: LY>YMJG>HSK>YCGK>SG. In contrast, the soil pH in the CK was 4.5, which was acidic. In particular, the application of LY had a significant effect on regulating the soil pH, and the soil pH (7.32) was 38.52 % higher than that of CK. Thus, the application of these materials has significant regulatory effects on soil pH. After applying the discarded agricultural and forestry resource materials, the soil organic matter content was significantly higher than that of CK (p<0.05), and the order of improving soil organic matter was as follows:YCGK>SG>HSK>LY>YMJG. The improvement effects of YCGK on soil organic matte were superior to those of other treatments, with an average content of 132.28 g·kg⁻¹, which was 2962.04% 2 962.04% compared to CK. This may be due to the abundance of cellulose, lignin, and various trace elements in YCGK, which could provide rich sources of organic matter to the soil. As well as the improvement effect of YCGK on soil available potassium, which was 4571.28 mg·kg⁻¹ with significant differences compared to other treatments. Overall, the comprehensive effects of YMJG on the soil matrix improvement of rare-earth tailings were the best, with soil TN, TP, TK, AN, and AP increasing by 971.43, 150, 9.46, 961.64, and 7765.32%, respectively. This may be attributed to the rich nutritional content of YMJG, including nitrogen and phosphorus, which possess a high nutritional value for soil matrix reconstruction. Pearson correlation analysis of soil physicochemical property indicators showed that soil pH was significantly positively correlated with soil conductivity, TN, and AN in the different treatments (p<0.05), with mutual and synergistic effects. The community structure and diversity of soil bacteria were significantly changed using different materials, as shown by high-throughput genome sequencing, and there were certain differences in the composition and structure of soil microbial communities among different treatments, with a total of 353 core OTUs. Among them, there were 2605 unique OTUs in LY, which was higher than those in the other treatments. The dominant bacterial community composition at each level of the five different treatments was similar, and consisted of Proteobacteria, Actinobacteria, Acidobacteria, Bacteroidetes, Chloroflexi, and other phyla. However, there were differences in the relative abundances of each treatment. First, the HSK and YCGK treatments significantly increased the relative abundances of Bacteroidetes and Micropepsaceae. The composition of the dominant horizontal bacterial communities was similar among the treatments at the phylum level. The first dominant microbe was Proteobacteria and the dominant microbe was Burkholderiaceae at the family level. From the comparison of data between different treatments, the HSK treatments had the highest Shannon indices, whereas YMJG had the greatest impact on bacterial abundance. Principal Component Analysis (PCA) showed that the soil microbial community structures of CK, YCGK, and SG were similar, while the soil microbial community structures of HSK and LY were relatively similar. There were significant differences in the soil microbial community structure between the YMJG and the other treatments. The clustering heatmap of the species abundance of soil bacteria in different treatments within the genus classification level showed that the Hyphomicrobium and Devosia genera had higher concentrations in soil samples from YMJG, HSK, and LY. This study showed that the five tested materials promoted the soil microbial metabolic activity and species richness of the bacterial communities in the reconstructed soil. These results proved that the tested materials had a certain promoting effect on optimizing the species richness of microorganisms in the soil. The increase in the number of microbial bacteria in the improved soil was an important manifestation of the improvement in the soil environmental quality. In summary, the slected materials have the advantages of being environmentally friendly, harmless, easy to obtain, processable, and inexpensive. At the same time, these materials not only increased soil pH and conductivity but also significantly increased soil nutrient content and improved bacterial colony structure in the soil, thereby optimizing soil ecological functions and creating conditions for accelerating the process of vegetation restoration. Based on the conditions of this experiment, we believe that YMJG is more conducive for improving the soil matrix of mining ore tailings, with significant advantages and good application prospects. This research could be used for soil organic matter enrichment in rare earth mining area reconstruction, and for agriculture and forestry waste resource utilization to provide a theoretical basis and technical reference.

Key words: ionic rare earth mining ore tailing, vegetation ecological restoration, agricultural and forestry waste, soil nutrients, soil microorganism