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With the rapid development of industry, Cr has become one of the major heavy metal pollutants in soil, severely impacting soil microecology, among which rhizosphere microorganisms can improve the soil microenvironment to promote plant growth. However, how rhizosphere bacterial communities respond to Cr stress under different cultivation modes remains to be further studied. Therefore, in this study, a greenhouse pot experiment combined with 16S rRNA high-throughput sequencing technology was used to study the effects of Cr stress at 200 mg kg−1 on the bacterial community structure and diversity in the rhizosphere soil of Iris tectorum under different cultivation modes. The results showed that the rhizosphere bacterial community diversity index (Shannon and Simpson) and abundance index (Ace and Chao) increased significantly with wetland plant diversity under Cr stress. Moreover, the bacterial community changed by 20.1% due to the addition of Cr, further leading to a 15.9% decrease in the common species of the bacterial community, among which Proteobacteria, Actinobacteria, Chloroflexi, and Acidobacteriota accounted for more than 74.8% of the total sequence. However, with the increase in plant diversity, the abundance of rhizosphere-dominant bacteria and plant growth-promoting bacteria communities increased significantly. Meanwhile, the symbiotic network analysis found that under the two cultivation modes, the synergistic effect between the dominant bacteria was significantly enhanced, and the soil microenvironment was improved. In addition, through redundancy analysis, it was found that C, N, and P nutrients in uncontaminated soil were the main driving factors of bacterial community succession in the rhizosphere of I. tectorum, and Cr content in contaminated soil was the main driving factor of bacterial community succession in I. tectorum rhizosphere. In summary, the results of this study will provide a basis for the response of the rhizosphere bacterial community to Cr and the interaction between wetland plants and rhizosphere bacteria in the heavy metal restoration of wetland plants under different cultivation modes.

Arbuscular mycorrhizal fungi (AMF) can improve plant tolerance to heavy metal stress in terrestrial ecosystems. However, in wetland ecosystems, AMF can improve the tolerance of wetland plants to heavy metals by changing the structure and composition of rhizosphere bacterial communities, which is still rarely studied. In this study, we investigated the effects of AMF on the structure and composition of bacterial communities in the rhizosphere of plants under different chromium concentrations. The results showed that Cr(Ⅵ) concentration in Acorus calamus. rhizosphere soil decreased by 12.6 % (5.6–21.7 %) on average after AMF inoculation, At the same time, it promoted the uptake of nutrients by A. calamus and increased soil carbon input. In addition, Cr stress decreased the bacterial community diversity and abundance index by 9.8 % (1.6–18.1 %) and 24.5 % (17.3–27.6 %) on average. On the contrary, the rhizosphere soil bacterial diversity and abundance index increased by 7.3 % (2.2–19.1 %) and 13.9 % (6.0–20.9 %) on average after AMF inoculation. Moreover, compared with the non-inoculated AMF group, the bacterial community structure of A. calamus rhizosphere changed by 24.6 % under Cr stress, The common number of species increased by 6.4 %. In addition, after inoculation of AMF significantly promote the growth of a large number of bacteria related to organic degradation, plant growth, and oxidative stress, increased soil carbon input improved the soil microenvironment. Meanwhile, After AMF inoculation, the Number of edges, Number of Nodes, Average degree, and Average Path length in the symbiotic network of rhizosphere soil bacterial community increased by 34.6 %, 10 %, 44.3 %, and 26.4 %, respectively. Therefore, it offers a possibility that AMF can enhance the tolerance of wetland plants to soil Cr pollution by improving the structure and composition of bacterial communities in the rhizosphere soils of wetland plants, which provide a basis for wetland plants to repair soil Cr pollution.

Ancient manganese (Mn) deposits are primarily characterized by the presence of Mn(II) carbonates that likely formed by the diagenetic reduction of precursor Mn(IV) oxides. As such, Precambrian sedimentary Mn deposits have been used as a line of evidence for the evolution of oxygen in Earth's surface environments. However, recent studies have shown that these Mn(II)-carbonates have the ability to directly accumulate within anoxic water columns, where free oxygen does not play a role in their formation. This alternative pathway casts uncertainty on the robustness of using ancient Mn deposits to constrain the redox fabric of the past marine water columns. Here, we investigate the Wafangzi Mn and Fe ore deposit from the 1.45 billion-year-old Tieling Formation, North China. The deposit contains Mn(II,III) mineral phases (hausmannite, braunite) as inclusions, or unreacted residues, trapped within Mn(II) carbonate (Ca-rhodochrosite). Some nodules and oolites of Mn(II) and Fe(II)-carbonate phases are also present and display a banded structure with concentric rings. Mn(III) oxide (manganite) is present in a paragenetic assemblage along with hematite and replacement textures with braunite. The negative carbon isotope composition (δ13C, –7‰ to –4‰) from Mn(II) carbonate samples in the Wafangzi Mn deposit which are distinct from that of contemporaneous seawater (~0‰), along with petrographic and speciation analyses, collectively suggest that the Mn(II,III)- and Fe(II)-bearing mineral phases formed through the diagenetic reduction of primary Mn(IV)/Fe(III) minerals coupled to the oxidation of organic matter. Therefore, the Wafangzi Mn deposit suggests the presence of sufficiently oxygenated marine waters, overlying anoxic ferruginous deeper waters with a transitional manganous water layer that could have driven the redox cycling of Mn, Fe, and C. Given the contemporaneous economic Mn deposits in the 1.45 Ga Ullawarra Formation in Western Australia, our findings imply the existence of a transient, and perhaps widespread, pulsed oxygenation event in the mid-Proterozoic oceans. [ABSTRACT FROM AUTHOR]

Sediment transport serves as a link for material exchange between land and sea. Using sediment traps, we can observe the capture and transport processes of sediments. Based on the sediment particle size distribution characteristics in Jiaozhou Bay, this paper analyzes the influence of a newly designed 3D sediment trap on the water–sand two-phase flow process inside and outside a trap device during its operation. Meanwhile, under a certain concentration condition, a numerical formula model is researched and proposed to evaluate the impact of the device's structure, the environmental flow speed, and the particle size on particle capture efficiency. This model is based on the CFD-DPM coupling in Fluent 2021R1 software, and the particle filtration process is solved using a combination of porous media and UDF functions. Finally, by analyzing the distribution of sediment movement in the fluid domain, two concepts, namely the percentage of particles entering the tube and the effective capture rate, are proposed. Suggestions for optimizing the structure of the trap are put forward to achieve optimal capture effects. [ABSTRACT FROM AUTHOR]