Prediction of Soil Clay Content and Cation Exchange Capacity Using Visible Near-Infrared Spectroscopy, Portable X-ray Fluorescence, and X-ray Diffraction Techniques

Effect of composite organic amendment on Cd(II) ions stabilization and microbial activity under various ammonium sulfate levels

To attenuate the risk of Cadmium(Cd) contamination and the deterioration of soil quality caused by excessive nitrogen fertilizer application in greenhouse, a composite organic amendment (spend mushroom substrate and its biochar) was prepared to remedy Cd(II) ions contaminated soil (0.6 mg/kg) under different N fertilizer levels. The results showed that in the absence of a composite organic amendment, the soil pH decreased by 0.15 when the N level increased from 0.1 to 0.8 g N⋅kg-1. However, the pH increased by 0.86-0.91, the exchangeable Cd(II) ions content decreased by 26.0%-26.7%, the microbial biomass increased by 34.34%-164.46%, and the number of copies of the AOB gene increased by 13-20 times with the application of composite organic amendment and the increase of N level. Both Pearson correlation analysis and Mantel test demonstrated the reduction in Cd(II) ions availability, the restoration of soil properties and the increase in microbial biomass all contributed to the composite organic amendment, which is of importance for soil remediation under excessive N fertilizer.

Piriformospora indica colonization enhances remediation of cadmium and chromium co-contaminated soils by king grass through plant growth promotion and rhizosphere microecological regulation

Poor plant growth and low pollutant bioavailability in contaminated soils limit phytoremediation efficiency. Pot experiments were conducted to investigate the effects and mechanisms of Piriformospora indica inoculation on the phytoremediation of Cd-Cr co-contaminated soils from farmland using king grass. P. indica colonization increased plant biomass by 20.4-24.6% and enhanced Cd/Cr accumulation in root, stem and leave tissues. Root vascular cylinder and cortex were the major structures for Cd/Cr transportation in plants. The amounts of Cd and Cr extracted by king grass considerably increased in the presence of P. indica (by 31.5-88.9% and 22.4-38.4%, respectively), as did the removal efficiency of both metals from soils (by 13.2-32.2% and 23.2-33.5%, respectively). Cd/Cr phytoextraction was closely related to the contents of alkanes, lipids and acids in root exudates. Following inoculation, the respiration of microbial sulfur compounds was promoted in soils at low and medium pollution levels, whereas nitrogen fixation and nitrification were reduced at high pollution level. This study demonstrates that P. indica inoculation enhances the phytoremediation efficiency of king grass for Cd-Cr co-contaminated soils through multiple regulation of plant growth, rhizosphere environment, root exudation and soil microbial function.

Enhanced methane oxidation efficiency by digestate biochar in landfill cover soil: Microbial shifts and carbon metabolites insights

The ability of biochar to enhance the oxidation of methane (CH4) in landfill cover soil by promoting the growth and activity of methane-oxidizing bacteria (MOB) has attracted significant attention. However, the optimal characteristics of digestate-derived biochar (DBC) for promoting the MOB community and CH4 removal performance remain unclear. This study examined how the CH4 oxidation capacity and respiratory metabolism of MOB life process are affected by the application of DBC compared with the most commonly used woody-derived biochar (WBC). The addition of both WBC and DBC enhanced CH4 oxidation, with DBC exhibiting a nearly twofold increase in cumulative CH4 oxidation mass (7.14 mg CH4 g-1) compared to WBC. The high ion-exchange capacity of DBC was found to be more favorable for the growth of Type I MOB, which have more efficient metabolic pathways for CH4 oxidation. Type I MOB which are abundant in DBC may prefer monovalent positive ions, while the charge-rich nature of DBC may also have hindered extracellular protein aggregation. The superiority of DBC in terms of CH4 oxidation thus highlights the underlying mechanisms of biochar-MOB interactions, offering potential biochar options for landfill cover soil.

Optical imaging spectroscopy coupled with machine learning for detecting heavy metal of plants: A review

Heavy metal elements, which inhibit plant development by destroying cell structure and wilting leaves, are easily absorbed by plants and eventually threaten human health via the food chain. Recently, with the increasing precision and refinement of optical instruments, optical imaging spectroscopy has gradually been applied to the detection and reaction of heavy metals in plants due to its in-situ, real-time, and simple operation compared with traditional chemical analysis methods. Moreover, the emergence of machine learning helps improve detection accuracy, making optical imaging spectroscopy comparable to conventional chemical analysis methods in some situations. This review (a): summarizes the progress of advanced optical imaging spectroscopy techniques coupled with artificial neural network algorithms for plant heavy metal detection over ten years from 2012-2022; (b) briefly describes and compares the principles and characteristics of spectroscopy and traditional chemical techniques applied to plants heavy metal detection, and the advantages of artificial neural network techniques including machine learning and deep learning techniques in combination with spectroscopy; (c) proposes the solutions such as coupling with other analytical and detection methods, portability, to address the challenges of unsatisfactory sensitivity of optical imaging spectroscopy and expensive instruments.

Remediation of cadmium contaminated soil by composite spent mushroom substrate organic amendment under high nitrogen level

Cadmium (Cd) contamination in soil poses a serious threat to ecological environment and crop quality, especially under high nitrogen level. Here, the efficiency of composite organic amendment (spent mushroom substrate and its biochar) on remediation of Cd contaminated soil under high nitrogen level has been studied through a 42 days' soil incubation experiment. The results showed: (i) the application of composite organic amendment minimized the repercussions of high nitrogen and significantly reduced the exchangeable Cd proportion by 28.3%-29.5%, especially for Ca(NO₃)₂ treatment; (ii) the application of composite organic amendment improved the physicochemical properties of soil, such as pH, CEC and organic matter content increased by 0.63-0.99 unit, 39.69%-45.00% and 7.77%-11.47%, and EC decreased by 16.21%-44.47% compared with non-amendment Cd-contaminated soil, respectively; (iii) the application of composite organic amendment significantly increased the soil enzyme activities and microbial biomass, among which urease activity was increased most by 12.06-16.42 mg·g^-1·d^-1, and the copy number of AOA was decreased by 30.6%- 92.0%, and the copy number of AOB was increased most by about 45 times. In brief, the composite organic amendment can alleviate the adverse effects of Cd and nitrogen on the soil, but its long-term efficacy needs to be verified in further field study.