Predicting Cd accumulation in rice and identifying nonlinear effects of soil nutrient elements based on machine learning methods.

The spatial mismatch of Cd content in soil and rice causes difficulties in environmental management for paddy soil. To investigate the influence of soil environment on the accumulation of Cd in rice grain, we conducted a paired field sampling in the middle of the Xiangjiang River basin, examining the relationships between soil properties, soil nutrient elements, Cd content, plant uptake factor (PUFCd), and translocation factors in different rice organs (root, shoot, and grain). The total soil Cd (CdT) and available Cd (CdA) contents and PUFCd showed large spatial variability with ranges of 0.31-6.19 mg/kg, 0.03-3.07 mg/kg, and 0.02-3.51, respectively. Soil pH, CdT, CdA, and the contents of soil nutrient elements (Mg, Mn, Ca, P, Si, and B) were linearly correlated with grain Cd content (Cdg) and PUFCd. The decision tree analysis identified nonlinear effects of Si, Zn and Fe on rice Cd accumulation, which suggested that low Si and high Zn led to high Cdg, and low Si and Fe caused high PUFCd. Using the soil nutrient elements as predictor variables, random forest models successfully predicted the Cdg and PUFCd and performed better than multiple linear regressions. It suggested the impacts of soil nutrient elements on rice Cd accumulation should receive more attention.

The Improvement in Hydrogen Storage Performance of MgH2 Enabled by Multilayer Ti3C2.

MgH2 has become a hot spot in the research of hydrogen storage materials, due to its high theoretical hydrogen storage capacity. However, the poor kinetics and thermodynamic properties of hydrogen absorption and desorption seriously hinder the development of this material. Ti-based materials can lead to good effects in terms of reducing the temperature of MgH2 in hydrogen absorption and desorption. MXene is a novel two-dimensional transition metal carbide or carbonitride similar in structure to graphene. Ti3C2 is one of the earliest and most widely used MXenes. Single-layer Ti3C2 can only exist in solution; in comparison, multilayer Ti3C2 (ML-Ti3C2) also exists as a solid powder. Thus, ML-Ti3C2 can be easily composited with MgH2. The MgH2+ML-Ti3C2 composite hydrogen storage system was successfully synthesized by ball milling. The experimental results show that the initial desorption temperature of MgH2-6 wt.% ML-Ti3C2 is reduced to 142 °C with a capacity of 6.56 wt.%. The Ea of hydrogen desorption in the MgH2-6 wt.% ML-Ti3C2 hydrogen storage system is approximately 99 kJ/mol, which is 35.3% lower than that of pristine MgH2. The enhancement of kinetics in hydrogen absorption and desorption by ML-Ti3C2 can be attributed to two synergistic effects: one is that Ti facilitates the easier dissociation or recombination of hydrogen molecules, while the other is that electron transfer generated by multivalent Ti promotes the easier conversion of hydrogen. These findings help to guide the hydrogen storage properties of metal hydrides doped with MXene.

Factors influencing the effectiveness of liming on cadmium reduction in rice: A meta-analysis and decision tree analysis.

Lime is widely applied as a soil amendment to reduce the grain cadmium (Cd) content in rice production. However, the effectiveness of liming on grain Cd reduction is inconsistent and often cannot meet the safety requirements established for rice production. To identify the factors causing the effectiveness of liming to vary, we collected data from peer-viewed articles regarding lime application in paddy soils that were published during the last ten years. The average Cd reduction rates in rice grains after liming were -44% across all the studies considered, which could be broken down into -48% for pot experiments only and -42% for field trials only. The results of a meta-analysis and decision tree analysis indicated that the experiment type (field or pot), lime dosage, lime type (CaCO3, Ca(OH)2, or CaO), soil environment factors (soil pH, soil available Cd content, soil total Cd, and Zn content), and rice cultivar all influenced the effectiveness of liming. Recommendations were made to guide future liming practice, e.g., (1) using a larger lime dosage when applied to soil with pH < 5.5, or soil with total Cd > 1 mg/kg or total Zn > 200 mg/kg; (2) using CaCO3 when applied with large dosages; and (3) planting low-Cd accumulation rice cultivars while applying lime. CAPSULE: A meta-analysis showed that the effectiveness of liming on rice grain Cd reduction was affected by the experiment type (field or pot), lime dosage, lime type, soil pH, rice cultivar, and soil total Cd and Zn content.