Pedosphere最新文献

Rare earth element (REE) mining has wrought severe ecosystem destruction, particularly in the loss of carbon (C), nitrogen (N), and phosphorus (P). Furthermore, its effects on nutrient recovery characteristics and associated microbial abundance are still poorly understood. In this study, an investigation was conducted to determine C, N, and P recovery patterns and microbial communities in abandoned REE mining tailings with different abandoned durations of 1.5 (1.5-Y), 7 (7-Y), 10 (10-Y), and 14 (14-Y) years and at an unmined site (the control group) in Jiangxi Province, China. Longitudinal tailing delamination at each site was investigated in 0–15 (layer 1) and 15–30 (layer 2) cm tailing layers. During the abandoned duration of REE tailings, C and P in layer 1 continued to recover from 1.62 to 8.51 g kg^-1 and from 0.71 to 1.94 g kg^-1, respectively; N losses of 0.60 and 0.22 g kg^-1 occurred at the 1.5-Y and 10-Y sites, while N in layer 1 slightly increased at the 14-Y site. Mesorhizobium, Methylosinus, Bradyrhizobium, Pseudomonas, and Azospirillum were dominant bacteria at the 14-Y site and in the control. The relative abundances of N-fixing bacteria Mesorhizobium (32.94%), Sinorhizobium (0.24%), Frankia (0.71%), and Burkholderia (2.38%) at the 14-Y site were 1.33–3.97 times those in the control (24.19%, 0.18%, 0.32% and 0.60%, respectively), which was helpful for tailing N recovery. At the 14-Y site, Tylospora (50.24%), Luellia (11.02%), Tomentella (6.94%), and Chaetomium (4.34%) were the dominant fungal genera, while Tylospora (56.93%), Suillus (11.45%), and Penicillium (6.78%) predominated in the control. The relative abundance of the P-dissolving fungus Aspergillus at the 14-Y site (0.42%) was 4.2 times that in the control (0.1%), which may lead to the improved tailing P solubility. At the 14-Y site, woody plants such as Pinus massoniana and native pioneering herbs and ferns such as Dicranopteris dichotoma and Nephrolepis auriculata probably invaded from adjacent areas. This study unraveled the natural restoration of plant and microbial communities along with soil nutrient changes in abandoned REE tailings, thus providing a novel insight into ecological recovery and restoration after mining.

Straw return in situ, a common agronomic measure in China, has been widely used not only to increase crop yields and improve soil nutrients but also to remove polycyclic aromatic hydrocarbons (PAHs) from agricultural soils. Nevertheless, the safety risks of food crops (i.e., human health risk of wheat grains) grown in PAHs-contaminated agricultural soils amended with crop straw remain uncertain. A pot experiment was conducted in a PAHs-contaminated agricultural soil cultivated with winter wheat under different ratios of corn straw addition (0% (control, CK), 1%, 2.5%, and 5%, weight/weight). Results showed that corn straw addition significantly (P < 0.05) decreased PAH concentrations in rhizosphere soil, roots, straws, and grains by 48.32%–50.01%, 11.85%–42.67%, 9.78%–28.03%, and 14.16%–31.67%, respectively, compared with CK, whereas the transfer factors of PAHs from roots to straws were significantly (P < 0.05) increased. A correlation heatmap showed that PAH concentrations in roots, straws, and grains were positively (P < 0.01) correlated with those in rhizosphere soil. These indicated that corn straw decreased PAH accumulation in winter wheat due to the increase of PAH dissipation in the rhizosphere soil, although it enhanced PAH transfer in winter wheat. The incremental lifetime cancer risk (ILCR) model indicated that corn straw significantly (P < 0.05) decreased the human health risk of winter wheat grains by 29.73%–45.05%. Overall, corn straw apparently reduced PAH accumulation in winter wheat, ecological risk, and human health risk via enhancing PAH dissipation in the rhizosphere soil. These findings provide an important scientific basis and theoretical guidance for agricultural safety production.

The widespread application of copper oxide nanoparticles (CuO NPs) in agricultural production has caused growing concerns about their impact on crops. In this study, wheat root elongation was used to evaluate the toxic effect concentrations of CuO NPs in two soils with differing properties, collected from farmlands in Guangdong (GD) and Shandong (SD) provinces, China. Plant morphological and biochemical properties were also assessed to explore the toxicity mechanism of CuO NPs on wheat seedlings. The root elongation results revealed lower toxic effect concentration values in the plants grown in GD soil than in SD soil. Furthermore, the treatment with CuO NPs at 200 mg Cu kg^-1 significantly reduced wheat root and shoot biomass by 35.8% and 15.8%, respectively, in GD soil. Electron microscopy showed that CuO NPs deformed wheat roots and entered leaf cells, causing deformation and damaging the cell structure. The CuO NP treatments also decreased chlorophyll content, increased antioxidant enzyme activity, and increased membrane lipid peroxidation in wheat leaves. The addition of CuO NPs significantly reduced the Zn (by 17.3%) and Fe (by 26.9%) contents in the leaves of plants grown in GD and SD soils, respectively. However, the contents of Cu, Mg, and Mn were increased by 27.4%–52.5% in GD soil and by 17.9%–71.6% in SD soil. These results suggested that CuO NPs showed greater toxicity to wheat plants grown in acidic soil than in alkaline soil and that the adverse effects of CuO NP treatments on wheat seedlings were due to a combination of CuO NPs and released Cu²⁺.

Managed peatlands are a significant source of nitrous oxide (N₂O), a powerful greenhouse gas and stratospheric ozone depleter. Due to the complexity and diversity of microbial N₂O processes, different methods such as tracer, isotopomer, and microbiological technologies are required to understand these processes. The combined application of different methods helps to precisely estimate these processes, which is crucial for the future management of drained peatlands, and to mitigate soil degradation and negative atmospheric impact. In this study, we investigated N₂O sources by combining tracer, isotopomer, and microbial analysis in a drained peatland forest under flooded and drained treatments. On average, the nitrification genes showed higher abundances in the drained treatment, and the denitrification genes showed higher abundances in the flooded treatment. This is consistent with the underlying chemistry, as nitrification requires oxygen while denitrification is anaerobic. We observed significant differences in labelled N₂O fluxes between the drained and flooded treatments. The emissions of N₂O from the flooded treatment were nearly negligible, whereas the N₂O evolved from the nitrogen-15 (¹⁵N)-labelled ammonium (¹⁵NH₄⁺) in the drained treatment peaked at 147 μg ¹⁵N m^-2 h^-1. This initially suggested nitrification as the driving mechanism behind N₂O fluxes in drained peatlands, but based on the genetic data, isotopic analysis, and N₂O mass enrichment, we conclude that hybrid N₂O formation involving ammonia oxidation was the main source of N₂O emissions in the drained treatment. Based on the ¹⁵N-labelled nitrate (¹⁵NO₃^-) tracer addition and gene copy numbers, the low N₂O emissions in the flooded treatment came possibly from complete denitrification producing inert dinitrogen. At atomic level, we observed selective enrichment of mass 45 of N₂O molecule under ¹⁵NH₄⁺ amendment in the drained treatment and enrichment of both masses 45 and 46 under ¹⁵NO₃^- amendment in the flooded treatment. The selective enrichment of mass 45 in the drained treatment indicated the presence of hybrid N₂O formation, which was also supported by the high abundances of archaeal genes.

This is the first study to report the co-occurrence of per- and polyfluoroalkyl substances (PFASs), heavy metals, and polycyclic aromatic hydrocarbons (PAHs) and their impacts on the native microbial consortium in soil due to the long-term exposure. The PFASs, heavy metals, and PAHs were detected in soil samples collected at 2–6 m below the ground surface at different sampling locations in a steel-making factory. The total concentrations of PFASs varied from 6.55 to 19.79 ng g^-1, with perfluorooctane sulfonate (PFOS), perfluorobutane sulfonate, and 6:2 chlorinated polyfluorinated ether sulfonate (alternative of PFOS) being the predominant PFASs. The concentrations of arsenic, cadmium, and lead were detected in the ranges of 4.40–1 270.00, 0.01–8.67, and 18.00–647.00 mg kg^-1, respectively, and the concentration of total PAHs was detected in the range of 1.02–131.60 mg kg^-1. The long-term exposure to mixed contaminants of PFASs, heavy metals, and PAHs led to lower richness and diversity of microbial communities in soil. The soil bacterial communities were mainly composed of Pseudomonas, norank_p_GAL15, Leptothrix, norank_o_Rokubacteriales, and Acinetobacter. Correlations between soil environmental factors and microbial communities indicated that cation exchange capacity and total phosphorus were two key factors in shaping the composition of native microbial communities. Furthermore, Arthrobacter, Leptothrix, and Sphingobium were found to be significantly positively correlated with PFAS concentrations, indicating that these genera could tolerate the stress exerted by PFASs, along with the stress imposed due to the presence of heavy metals or/and PAHs.

Roots and shells are two potential organs through which peanut plants absorb cadium (Cd) from soils; however, the relative contributions of the two uptake pathways (root uptake and shell absorption) to kernel Cd accumulation and their translocation characteristics are poorly understood. In this study, the relative contributions of the two pathways to Cd accumulation in two peanut cultivars, Xianghua2008 (XH) and Yueyou43 (YY), were accurately assessed by labeling rooting and podding zone soils with ¹¹³Cd and ¹¹¹Cd isotopes (0.3 mg kg^-1 dry soil), respectively, in a split-pot design. The results showed that approximately 96% of the Cd accumulated in the peanut kernels was derived from root uptake, while only 4% originated from shell absorption. Only 1% of the Cd accumulated in whole peanut plants was attributed to shell absorption, of which 41%–44% was retained in shells and 56%–59% was translocated to kernels. In contrast, the Cd absorbed by roots was efficiently translocated into all plant organs, of which 80%–84% was distributed in shoots. Although YY accumulated 1.3 times more Cd in whole plants than XH, the relative contributions of the two pathways to Cd accumulation in each plant organ were barely affected by peanut cultivars. Due to the strong retention effect of shells, shell-derived Cd was approximately 2 times higher than root-derived Cd in shells. These results would improve the understanding of Cd accumulation processes in peanut plants, revealing that the root uptake pathway contributes predominantly to the Cd concentration in peanut kernels, based on which strategies and technology for the reduction of Cd in peanut plants could be designed and developed.

Coastal marshes are transitional areas between terrestrial and aquatic ecosystems. They are sensitive to climate change and anthropogenic activities. In recent decades, the reclamation of coastal marshes has greatly increased, and its effects on microbial communities in coastal marshes have been studied with great interest. Most of these studies have explained the short-term spatiotemporal variation in soil microbial community dynamics. However, the impact of reclamation on the community composition and assembly processes of functional microbes (e.g., ammonia-oxidizing prokaryotes) is often ignored. In this study, using quantitative polymerase chain reaction and the Ion S5™ XL sequencing platform, we investigated the spatiotemporal dynamics, assembly processes, and diversity patterns of ammonia-oxidizing prokaryotes in 1 000-year-old reclaimed coastal salt marshes. The taxonomic and phylogenetic diversity and composition of ammonia oxidizers showed apparent spatiotemporal variations with soil reclamation. Phylogenetic null modelling-based analysis showed that across all sites, the archaeal ammonia-oxidizing community was assembled by a deterministic process (84.71%), and deterministic processes were also dominant (55.2%) for ammonia-oxidizing bacterial communities except for communities at 60 years of reclamation. The assembly process and nitrification activity in reclaimed soils were positively correlated. The abundance of the amoA gene and changes in ammonia-oxidizing archaeal and bacterial diversities significantly affected the nitrification activity in reclaimed soils. These findings suggest that long-term coastal salt marsh reclamation affects nitrification by modulating the activities of ammonia-oxidizing microorganisms and regulating their community structures and assembly processes. These results provide a better understanding of the effects of long-term land reclamation on soil nitrogen-cycling microbial communities.

The formation and growth of segregation ice dominate the frost heave during soil freezing, which is closely related to water migration. To analyze segregation ice during soil freezing for different soils, a freezing-thawing experiment was conducted with Lanzhou loess (LZL) and Qinghai-Tibet Plateau silty clay (QSC) using a novel layered nuclear magnetic resonance approach. During LZL freezing, the unfrozen water content first increased and then decreased with decreasing temperature near the freezing front, but decreased with decreasing temperature in other layers, whereas during the freezing of QSC, the unfrozen water content in different layers (including the freezing front) decreased with decreased temperature. Notably, the increased liquid water near the freezing front during LZL freezing was primarily adsorbed water. In addition to the temperature gradient, the squeezing action during soil freezing was another important factor affecting water migration, especially at the early stage of soil freezing. However, which of the two factors, squeezing action and temperature gradient, was the dominant one causing water migration depended on soil structure. At the early stage of soil freezing, the squeezing action had a significant effect on the water migration of LZL, but no significant effect on that of QSC. Furthermore, water accumulation of LZL near the freezing front due to squeezing action at the early stage of freezing limited the formation and growth of segregation ice. This study provided an improved understanding for ice segregation and water migration during soil freezing.