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In this study, the effectiveness of controlling the eutrophication using purple parent rock to cap the sediments was evaluated in the laboratory scale. Sediments were collected from Sanxikou reservoir (China) in July 2013. Then, three types of purple parent rock (T 1 f, J 3 p, and J 2 s) which are distributed widely in southwest China were used to cap the sediments. Limestone and calcite were used as the contrast group, because they had been reported as effective controls on eutrophication. Then, they were incubated at 20 °C for 46 days. The results indicated that the application of purple parent rock as a barrier material can effectively inhibit the release of nutrient elements in sediments, and the inhibition rates of total nitrogen (TN), total phosphorus (TP), ammonium (NH 4 –N), and nitrate (NO 3 –N) were much better than that of limestone and calcite. Among the three types of purple parent rock, J 3 p exhibited the best inhibitory effect on the release of nitrogen in sediments, and the inhibition efficiency of TN, NH 4 –N, and NO 3 –N was 59.7, 77.6, and 45.1%, respectively. As for T 1 f, it exhibited the best inhibitory effect on the release of TP in sediments with the inhibition rate of 94.4%. Whereas all these capping materials showed weak inhibition on release of organic matter in sediments, and the inhibition efficiencies were less than 20%. Moreover, these treatments could also cause distinct changes in the microbial community in sediments and overlying water, and the contents of TN and TP in all capping materials increased. All results demonstrated that purple parent rock could inhibit the release of nutrient in sediments through mechanical interception, physical adsorption, and chemical absorption as well as changing the microbial activity in the covering layer, sediments, or overlying water.

Summarized the heavy metal pollution caused by natural and human activities. The natural causes include the migration and redistribution of soil debris and the hydraulic migration of soil parent rock with high background value under the action of wind; human factors include mining, abandoned mining areas, fertilizer and pesticide application, and sewage irrigation. By examining the sources of heavy metals in soil, the temporal and spatial variation and source variation of heavy metal pollution can be summarized, and then find a reasonable way to intervene as early as possible from the origin to reduce the harm of this pollution to the soil. Finally, future research trends and key problems were indicated, which laid a theoretical foundation for further effective research.

Summary Soil is the primary source of plant silicon (Si) and therefore a key reservoir of the Si biological cycling. Soil processes control the stock of Si‐bearing minerals and the release of dissolved Si (DSi), hence the Si fluxes at the Earth's surface. Here, we review the interdependent relationship between soil processes and the return of plant Si in soils, and their controls on the biological Si feedback loop. Dissolution and precipitation of soil silicate minerals govern the bioavailability of Si. Plants affect Si biocycling through mineral weathering, root uptake, phytolith formation, return and dissolution in soil. Thus, soil processes and Si biocycling readily interact in soil–plant systems. Rock mineral weathering and soil formation are driven by the five soil‐forming factors: parent rock, climate, topography, age and biota. These factors govern Si fluxes in soil–plant systems since they impact both the mineral weathering rate and fate of DSi. The variability of soil‐forming factors at a global scale explains both the soil diversity and high variability of the rates of Si cycling in terrestrial ecosystems. Plants play a crucial role in soil evolution by promoting weathering and forming phytoliths (plant silica bodies). They thus act as Si sinks and sources. With increasing depletion of lithogenic (LSi) and pedogenic (PSi) silicates, the biological Si feedback loop progressively takes over the Si plant uptake from weatherable LSi and PSi minerals. With rising weathering, the soil becomes increasingly concentrated in phytoliths, phytogenic amorphous silicates (PhSi), which are constantly formed in plant and dissolved in soil. Paradoxically, the Si biocycling is thus more intense in soils depleted in primary LSi source. By converting soil LSi and PSi into PhSi, plants increase the mobility of Si in soil and alleviate desilication in the topsoil. Non‐essential plant Si is therefore an essential link between mineral and living worlds. The dynamics of Si in terrestrial ecosystems is thus largely governed by pedogenesis and its relationship with plant community and diversity. Consequently, the appraisal of soil constituents and processes is central to further understand their interaction with the biological Si feedback loop. Lay Summary

The aim of the study was to characterize pedogenic iron forms in the sediments of the Lower Triassic (Buntsandstein) in the north-eastern part of the Holy Cross Mountains. These are sediments of continental origin and unique features as the so-called ‘red beds’. Three main types of rocks were studied – sandstones, mudstones and claystones. Chemical forms of iron: Fe (XRF), Fe (6M HCl), Fe (dithionite-citrate-bicarbonate, DCB), Fe (ammonium oxalate), Fe (sodium pyrophosphate) were determined. The XRD method revealed the occurrence of goethite in sandstones and hematite in mudstones and claystones. Differential XRD (DXRD) analysis did not show the presence of amorphous iron minerals. The average Fe content in sandstones was 83 g·kg , in mudstones 47 g·kg , in claystones 55 g·kg , while there were lower concentrations of Fe (66 g·kg , 13 g·kg , 26 g·kg , respectively). Fe form content was in the range of 0.3–4 g·kg–1, while there were only traces of Fe . Only Fe and Fe occurred in good correlation. In the pedogenic interpretation of the studied rocks, mutual relations between chemical forms of iron were used and their reference to the identified iron minerals. Siltstones and claystones have high resistance to pedogenic factors, which is indicated by low release rates Fe :Fe and very low amorphization index Fe :Fe . The reason is the presence of well crystalline hematite in these rocks. In sandstones, resistance is conditioned by the occurrence of goethite in the matrix. Chemical destruction of iron-carbonate cement promotes the release and amorphization of iron in soils developed from sandstones. The presented results indicate that the specificity of Lower Triassic rocks is important for the proper classification and assessment of properties of soils with a characteristic red colour.

Background and aims Ultramafic soils constitute an extreme environment for plants because of specific physico-chemical properties and the presence of Ni, Cr, and Co. We hypothesized that type of ultramafic parent rock depending on their origin affects the composition of soils and plants. Therefore, phytoavailability of metals would be higher in soil derived from serpentinized peridotite compared to serpentinite because of differences in susceptibility of minerals to weathering. Results Based on DTPA-CaCl2 extractions, we noted that soil derived from the serpentinized peridotite is characterized by a higher phytoavailability of Ni compared to soil derived from the serpentinite. On the contrary, plant species growing on soil derived from the serpentinite contain higher concentrations of metals. Conclusions Our study suggests that the metal uptake by plants is controlled by the mineral composition of parent rocks, which results from both their original magmatic composition and later metamorphic processes. Chemical extractions show that the phytoavailability of Ni and Co is higher in soil derived from the serpentinized peridotite than the serpentinite. Surprisingly, plants growing on the soil derived from the serpentinite contain higher levels of metals compared to these from the serpentinized peridotite derived soil. This contrasting behavior is due to higher abundances of Ca and Mg, not only Ni and Co, in soil derived from the serpentinized peridotite as compared to those in the soil derived from the serpentinite. Calcium and Mg are favored by plants and preferably fill the available sites, resulting in low Ni and Co intake despite their higher abundances.

Few studies have investigated the potential amount of Cd needing remediation in karst soils, despite the importance of such strategies for managing and restoring Cd-polluted soils. This study focuses on a typical karst region in Guangxi, China, where 12,547 surface soil samples and 48 soil profiles (collected every 20 cm from 0 to 200 cm depth) were analyzed. We conducted a comprehensive analysis of Cd in these soils and developed a formula for determining the necessary remediation. The findings indicated that the baseline concentration of Cd in surface soils was 0.383 mg/kg, demonstrating a wide-ranging variability, with content spanning from 0.031 to 16.192 mg/kg. Notably, the depth-wise distribution of Cd in the soils showed an extensive range from the detection limit up to 8222 mg/kg. The regional distribution of Cd generally showed higher concentrations in the southwest and lower concentrations in the northeast, as revealed by principal component analysis linking Cd sources to soil parent material characteristics, agricultural activities, and industrial activities. One-way analysis of variance indicated significant influences of soil type, soil use, and topography on surface soil Cd concentrations, whereas soil type, topography, and parent rock material significantly affected deep soil Cd concentrations. Analysis of the Cd distribution patterns revealed a logarithmic distribution trend with increasing depth. Consequently, a logarithmic model was fitted to derive a formula for the potential remediation requirements of Cd. The formula for estimating potential Cd repair was deduced and summarized, enabling the calculation of potential Cd repair under different land use modes, parent material types and soil types. The formula is scientifically sound, representative, and innovative. These methods offer scientific guidance for the control, remediation, and production practices in relation to Cd-contaminated soils in the karst region and can be applied in karst regions globally.

The parent rock inheritance of the purple soils in the Sichuan Basin is evident, and this is due to factors that are directly related to the parent rocks’ characteristics. Fundamentally, the nature of purple soils is determined by the lithology, chemical composition, weathering, and soil formation of parent rocks, whereas the provenance, and tectonic context of rocks during their diagenesis have a significant influence on their rock attributes. In this study, rocks from four sedimentary layers of the Cretaceous and Jurassic eras – k1c, J3p, J3s, J2s in the Sichuan Basin – as well as the overlying soils were examined, and experimental determinations of the samples’ physical characteristics and chemical elemental composition were made to confirm the parent rock inheritance of purple soils. The essential weathering indices ICV, CIAcorr, WIP, and Na/K were used to study the weathering characteristics of the rocks and soils, and the A-CN-K ternary diagram was used to assess the weathering trends of the rocks. The findings demonstrate that purple soil exhibits significant parent rock inheritance due to its rapid physical soil formation process and weak chemical weathering process. That the rocks of the four sedimentary layers in the study area have all reached a moderate degree of weathering, their original source components are quartzose sedimentary which may have been derived from feldspar source rocks. The tectonic background of the source rocks may be mainly continental arc and active continental margin environment, there may be an oceanic arc tectonic environment.

Parent rock is a key factor contributing to differences in soil physical and chemical properties. However, the mechanism of microbial carbon cycle mediated by soils with different physical and chemical properties based on parent rock are unclear. In this study, the physical and chemical properties of weathering soils of different parent rocks and the characteristics of soil carbon content were analysed. The composition of soil bacteria and fungi and the genes associated with carbon cycle were analysed via genome sequencing. The results showed that the highest abundance and diversity of soil microbes was detected in purple sandstone, followed by limestone and the least in basalt. Further, the predominant bacterial phyla in the three parent rocks were Proteobacteria, Chloroflexi, Acidobacteria, and Actinobacteria. The predominant fungi were those belonging to phyla Basidiomycota, Ascomycota, and Mortierellomycota. Soil organic carbon (SOC) and available nitrogen (AN), available potassium(AK) and available phosphorus (AP) were the main factors affecting the composition of soil bacteria, while soil soil water content (SWC) pH and AP were the main factors affecting the composition of soil fungi. Similarly, the relative abundance of functional genes associated with soil carbon cycle was the greatest in the purple sandstone, followed by limestone and the least in basalt. The variation in relative abundance of the genes was correlated with the soil physico-chemical properties, especially soil SWC, pH, and AP, which limited carbon metabolism of the soil microbes. Our results show that soil physical and chemical properties of the parental rock regulate microbial composition and carbon cycling.

In order to study the distribution of selenium in surface soil and its main influencing factor, we collected 360 surface soil samples and four groups of soil profiles with 210 corresponding parent rock samples in Langao County, Shaanxi Province (a typical high-selenium area of Daba Mountain). Samples were analyzed for trace elements by using ICP-MS, ICP-OES and HG-AFS. The results show the following. (1) selenium content in surface soils of Langao County varies greatly (0.03–16.96 mg/kg). The mean selenium content in surface soils of Langao County is 0.99 mg/kg, higher than the global (0.4 mg/kg) and China (0.29 mg/kg) soil average, and 3.4 times the mean of soil selenium in China. (2) Selenium content of bedrock in Langao County also varies greatly (0.01–56.22 mg/kg), with an average selenium content of 2.02 mg/kg, which is 40 times higher than the upper crust (0.05 mg/kg). (3) Selenium content in the strata of the Late Precambrian–Early Paleozoic and its variation is an important factor affecting the spatial variation of soil selenium content. The black rock series (carbonaceous slate and silicon-bearing carbonaceous slate) of the Upper Ediacaran–Cambrian on the north side has the highest mean selenium content (> 7.92 mg/kg), and the selenium content of the surface soil in the distribution area can reach up to 16.96 mg/kg. The Middle Cambrian, Upper Cambrian, Ordovician and Silurian (limestone and marl) in the south has the lowest mean selenium content (< 2 mg/kg), and the selenium content of surface soil in the distribution area is lower than 0.8 mg/kg mostly. (4) Soil samples at different depths in the same soil profile have similar composition of rare earth elements (REE), and bedrock and corresponding topsoil has similar composition of REE. This study indicates the selenium content in the topsoil varies greatly, even in high-selenium area. And the difference of selenium distribution is closely related to the original selenium content of the bedrock.

AIMS: We investigated how outcrops of different geological origins enhance the plant megadiversity of the Atlantic rainforest hotspot. METHODS: We collected vegetation, topographic, and soil fertility data from 50 2 m² plots in each of nine rock outcrops (three ironstones -or cangas, three quartzites and three granitoids) in the Iron Quadrangle, SE Brazil. We examined the response of community diversity and structure patterns to edaphic and topographic gradients by means of diversity profiles, clustering and ordination analyses. Species were organized into nine functional groups. RESULTS: We inventoried 17,690 individuals belonging to 352 species. Functional groups with largest cover were sclerophytic shrubs (in cangas), graminoid and poikilohydric herbs (in both granitoids and quartzites). Granitoid plant communities were the least diverse, on account of fewer substrate types leading to more xeric conditions. The multivariate analyses sorted the outcrops by geological origin, although within-lithotype similarity was low. There was stronger similarity between cangas and quartzites, separated from granitoids. Soil was nutrient-poor, and variables most influencing this pattern were number of substrates, topographic heterogeneity, soil depth, and aluminum saturation. CONCLUSIONS: Saxicolous plant communities responded more strongly to microtopographic than soil fertility parameters. Each lithotype contributes differently to the high alpha- and especially beta-diversity within the Atlantic Rainforest matrix.