Yong Liu

Preparing red mud/phosphogypsum-based artificial soils for vegetation restoration is promising. However, how artificial soil develops during vegetation restoration is unclear, especially regarding the relationship between the bacterial community and the development of artificial soil. The bacterial community changes in the early-stage engineering simulation of red mud/phosphogypsum-based artificial soil vegetation restoration were analyzed for the first time in this paper. The results showed that the structure of the bacterial community was simple at the beginning, mainly consisting of Proteobacteria, Firmicutes, and Bacteroidota, with total abundances of 74.5% and 89.3% in the two plots, respectively. The richness, diversity, and evenness of the bacterial communities all significantly increased over time (p < 0.05), indicating that the compositions of the bacterial communities in artificial soils undergo constant development, adjustment, and optimization. There were good correlations between bacterial communities and environmental factors (e.g., pH, W_H2O, OM, TN, TK, AK, TP), which generally reflected the significant synergistic development and interaction between the quality of the soil environmental and bacterial communities. There were complex dynamic changes in the functions of the bacteria during the development of artificial soils, which were mainly reflected in the decline in the abundances of chemoheterotrophy, aerobic chemoheterotrophy, and animal parasites or symbionts, but there was an increase in the abundances of phototrophy, cyanobacteria, and dark sulfide oxidation. This reflects the highly active physiological and biochemical reaction functions of bacterial communities in the development of artificial soils, which is of great significance for continuously enhancing the fertility quality and ecological attributes of artificial soils.

Silicon (Si) is one of the biogenic elements in lake aquatic ecosystems. Sediments are both sinks and sources of Si, but little is known about its influence on the biogeochemical cycle of Si in lakes and its relationship to other biogenic factors such as carbon and nitrogen. Examining Caohai Lake, a typical macrophytic lake in China, this study systematically examined the different Si forms and biogenic silica (BSi) distribution characteristics and their coupling relationships with total organic carbon (TOC) and total nitrogen (TN) in surface sediments. Iron–manganese-oxide-bonded silicon (IMOF-Si) and organic sulfide-bonded silicon (OSF-Si) jointly accounted for 95.9% of Valid-Si in the sediments, indicating that the fixation of Si by organic matter and iron–manganese oxides was the main mechanism underlying the formation of the different forms of Valid-Si in sediments. The release and recycling of Si in sediments may be mainly driven by mineralized degradation of organic matter and anoxic reduction conditions at the sediment–water interface. The content of biogenic Si (BSi) in the sediments was relatively higher in the southern and eastern areas, which could be explained by the intensification of eutrophication and the increased abundance of diatomaceous siliceous organisms in these areas seen in recent years. The TOC and TN contents in the sediments were generally high, and the sources of organic matter in the sediments included both the residues of endophytes (main contributors) and the input of terrigenous organic matter. TOC and TN both had highly significant correlations with OSF-Si and Valid-Si, which demonstrated that Valid-Si had excellent coupling relationships with C and N in the sediments. The good correlation between BSi, TOC and TN (p < 0.01), as well as the high C/Si, N/Si mole ratio of TOC and TN to BSi, respectivelny, indicating that the dissolution and release rate of BSi may be much higher than the degradation rate of organic matter from the sediments, especially in the areas with a higher abundance of siliceous organisms.

Red mud and phosphogypsum are two typical industrial by-products. The preparation of red mud/phosphogypsum-based artificial soils offers a promising novel solution to the efficient synergistic disposal of them. Fungi, as key drivers, can promote the continuous development and ecological improvement of artificial soils. This study is first to report the characteristics of fungal communities in three artificial soils after one year of incubation. The preliminary formation of fungal communities (with relatively low diversity) resulted in a total of 3 fungal phyla, 81 fungal genera, and 144 operational taxonomic units (OTUs) in artificial soils. Ascomycota was the dominant fungal phylum in each artificial soil (>99.5%), and the high-abundance fungal genera included Unclassified_c_Sordariomycetes, Unclassified_o_Sordariales, Emericellopsis, Kernia, Unclassified_f_Nectriaceae, Ramophialophora, Schizothecium, and Iodophanus. There were significant differences among the three artificial soils in the compositions of fungal genera, which affected material cycling, ecological succession, and soil development and maturation to varying extents. According to the FUNGuild prediction of fungal communities, saprotrophic fungi (such as undefined saprotroph, dung saprotroph–undefined saprotroph, and dung saprotroph) played dominant roles in promoting the degradation and humification of organic matter and the cycling of carbon in artificial soils. Fungal communities in the three artificial soils had strong correlations with many environmental factors (such as pH, organic matter, available nitrogen, total nitrogen, available phosphorous, sucrase, urease, acid phosphatase, alkaline phosphatase, and catalase), indicating significant interactions between them. This is not only conducive to the continuous optimization of the structure of fungal communities in artificial soils but also promotes the balanced and homogeneous distribution of various substances, promoting continuous soil development and maturation and gradual improvement in its ecological functions. This study provides an important scientific basis for clarifying the mechanisms of mycogenesis during the continuous development and maturation of artificial soils.

The preparation of artificial soil is a potential cooperative resource utilization scheme for red mud and phosphogypsum on a large scale, with a low cost and simple operation. The characteristics of the bacterial community structure and function in three artificial soils were systematically studied for the first time. Relatively rich bacterial communities were formed in the artificial soils, with relatively high abundances of bacterial phyla (e.g., Cyanobacteria, Proteobacteria, Actinobacteriota, and Chloroflexi) and bacterial genera (e.g., Microcoleus_PCC-7113, Rheinheimera, and Egicoccus), which can play key roles in various nutrient transformations, resistance to saline–alkali stress and pollutant toxicity, the enhancement of various soil enzyme activities, and the ecosystem construction of artificial soil. There were diverse bacterial functions (e.g., photoautotrophy, chemoheterotrophy, aromatic compound degradation, fermentation, nitrate reduction, cellulolysis, nitrogen fixation, etc.), indicating the possibility of various bacteria-dominated biochemical reactions in the artificial soil, which can significantly enrich the nutrient cycling and energy flow and enhance the fertility of the artificial soil and the activity of the soil life. The bacterial communities in the different artificial soils were generally correlated with major physicochemical factors (e.g., pH, OM, TN, AN, and AP), as well as enzyme activity factors (e.g., S-UE, S-SC, S-AKP, S-CAT, and S-AP), which comprehensively illustrates the complexity of the interaction between bacterial communities and environmental factors in artificial soils, and which may affect the succession direction of bacterial communities, the quality of the artificial soil environment, and the speed and direction of the development and maturity of the artificial soil. This study provides an important scientific basis for the synergistic soilization of two typical industrial solid wastes, red mud and phosphogypsum, specifically for the microbial mechanism, for the further evolution and development of artificial soil prepared using red mud and phosphogypsum.

Silicon (Si) is one of the main biogenic elements in the aquatic ecosystem of lakes, significantly affecting the primary productivity of lakes. Lake sediment is an important sink of Si, which exists in different Si forms and will be released and participate in the recycling of Si when the sediment environment changes. Compared to carbon (C), nitrogen (N) and phosphorus (P), the understanding of different Si forms in sediments and their biogeochemical cycling is currently insufficient. Dianchi Lake, a typical eutrophic lake in southwest China, was selected as an example, and the contents of different Si forms and biogenic silicon (BSi), as well as their correlations with total organic carbon (TOC), total nitrogen (TN), and chlorophyll a in the surface sediments, were systematically investigated to explore Si’s recycling characteristics. The results showed that the coupling relationship of the four different Si forms in the surface sediments of Dianchi Lake was poor (p > 0.05), indicating that their sources were relatively independent. Moreover, their formation may be greatly influenced by the adsorption, fixation and redistribution of dissolved silicon by different lake substances. The contents of different Si forms in the surface sediments of Dianchi Lake were ranked as iron-manganese-oxide-bonded silicon (IMOF-Si) > organic sulfide-bonded silicon (OSF-Si) > ion-exchangeable silicon (IEF-Si) > carbonate-bound silicon (CF-Si). In particular, the contents of IMOF-Si and OSF-Si reached 2983.7~3434.7 mg/kg and 1067.6~1324.3 mg/kg, respectively, suggesting that the release and recycling of Si in surface sediments may be more sensitive to changes in redox conditions at the sediment–water interface, which become the main pathway for Si recycling, and the slow degradation of organic matter rich in OSF-Si may lead to long-term and continuous endogenous Si recycling. The low proportion (0.3~0.6%) and spatial differences of biogenic silicon (BSi) in the surface sediments of Dianchi Lake, as well as the poor correlation between BSi and TOC, TN, and chlorophyll a, indicated that the primary productivity of Dianchi Lake was still dominated by cyanobacteria and other algal blooms, while the relative abundance of siliceous organisms such as diatoms was low and closer to the central area of Dianchi Lake. Additionally, BSi may have a faster release capability relative to TOC and may participate in Si recycling.

Macrophyte-dominated eutrophication (MDE) lakes have attracted wide attention due to the high phosphorus (P) loading in sediments that poses a wide spread risk for P release and pollution management. However, because of the superior productivity characteristics, the role of organic P mineralization in sediments in the internal P loading of MDE lake is still under debate. This study investigated the release dynamic of P in the sediments of Lake Caohai, a MDE lake in southwest of China, using a combination of the modified Huffer sequential extraction method, ³¹P nuclear magnetic resonance spectroscopy (NMR), and composite diffusive gradient in thin films (DGT) technology. Results showed that the apparent P diffusion flux at the sediment-water interface was remarkably high, with a mean value of 0.37 mg m⁻² d⁻¹. The phosphate ester organophosphorus components (i.e., Mono-P and Diester-P) continuously deposited and degraded in the sediments maintained the high productivity of the lake, and the mineralization process plays a critical role in the release of internal P. Although the content of inorganic P in sediment is relatively high (accounting for approximately 60% of total P), the reductive mechanism based on P-containing iron oxide/hydroxide has a low contribution to the internal P loading, as was indicated by the low release rate of P-combination iron-manganese (Fe-Mn)/iron-aluminum (Fe-Al) (BD-P and NaOH-P) and the insignificant positive correlations between DGT-labile P and DGT-labile Fe in the sediment cores. Additionally, organic P in sediments could transfer to P-combination Fe-Al/Fe-Mn. However, in severely expropriated environments, the enrichment of P-combination Fe-Al/Fe-Mn in surface sediments inhibited the mineralization of monophosphate to some degree. Taken together, this study emphasized the impact of sediment organic P loading on the release of internal P in lake, highlighting that organic P is also the valuable objects for avoiding eutrophication of MDE lakes.