Pedosphere最新文献

Paraquat and copper (Cu) are commonly used and detected in soil. Therefore, it is important to understand their mobility in the environment. In this study, the competitive effects of paraquat and Cu on their adsorption in five representative Chinese soils were investigated using batch adsorption equilibrium experiments and spectroscopic analysis. The results showed that the adsorption of paraquat in soil varied with soil type and was positively correlated with both soil cation exchange capacity and organic matter content. Paraquat exerted a more remarkable suppression effect on the adsorption of Cu than Cu on the adsorption of paraquat. In the presence of 0.12 and 0.19 mmol L^–1 paraquat, Cu adsorption decreased by 16% and 22% in Heilongjiang soil and by 24% and 37% in Jiangxi soil, respectively. In the presence of 0.1 and 0.2 mmol L^–1 Cu, paraquat adsorption decreased by 4% and 8% in Heilongjiang soil and by 15% and 19% in Jiangxi soil, respectively. Exchange selectivity involving symmetric cation (paraquat²+ and Cu²+) exchange is the probable basis for the suppression effect. The ultraviolet-visible absorption experiments suggested that the formation of Cu-paraquat complexes was unlikely to happen in a solution or at the soil surface. Copper K-edge X-ray absorption spectroscopy indicated that Cu in soil may have some water as hydration layers as the nearest neighbors, and each Cu atom was coordinated with five oxygen atoms. These findings greatly improve our knowledge of the molecular-scale adsorption mechanisms of paraquat and Cu in soil and can be used to predict the behavior, transport, and fate of paraquat and Cu in agricultural soils.

With global climate change, soil drying-rewetting (DRW) events have intensified and occurred frequently on the Loess Plateau of China. However, the extent to which the DRW cycles with different wetting intensities and cycle numbers alter microbial community and respiration is barely understood. Here, indoor DRW one and four cycles treatments were implemented on soil samples obtained from the Loess Plateau, involving increase of soil moisture from 10% water-holding capacity (WHC) to 60% and 90% WHC (i.e., 10%–60% and 10%–90% WHC, respectively). Constant soil moistures of 10%, 60%, and 90% WHC were used as the controls. The results showed that bacterial diversity and richness decreased and those of fungi remained unchanged under DRW treatments compared to the controls. Under all moisture levels, Actinobacteriota and Ascomycota were the most dominant bacterial and fungal phyla, respectively. The bacterial network was more complex than that of fungi, indicating that bacteria had a greater potential for interaction and niche sharing under DRW treatments. The pulse of respiration rate declined as the DRW cycle increased under 10%–60% WHC, but remained similar for different cycles under 10%–90% WHC. Moreover, the DRW treatments reduced the overall carbon loss, and the direct carbon release under 10%–60% WHC was larger than that under 10%–90% WHC. The cumulative CO₂ emissions after four DRW cycles were significantly positively correlated with microbial biomass carbon and negatively correlated with fungal richness (Chao 1).

Long-term excessive application of mineral fertilizer has led to soil acidification and phosphorus (P) accumulation, increasing the risk of P loss and environmental pollution, and cessation of fertilization is widely considered as a cost-effective management strategy to relieve this situation; however, how such cessation influences P speciation and concentrations in a bulk soil and colloidal fractions and whether decreasing P concentration might maintain soil fertility remain unclear. In this study, the effects of long-term fertilization (ca. 40 years) and short-term cessation of fertilization (ca. 16 months) on inorganic, organic, and colloidal P in lime concretion black soil were investigated using P sequential fractionation and ³¹P nuclear magnetic resonance spectroscopy. After long-term fertilization, available P, dicalcium phosphate, iron-bound P, orthophosphate monoesters, and orthophosphate diesters increased significantly, but soil pH decreased by ca. 2.8 units, indicating that long-term fertilization caused soil acidification and P accumulation and changed P speciation markedly. In contrast, short-term fertilization cessation increased soil pH by ca. 0.8 units and slightly reduced available and inorganic P. Available P after fertilization cessation was 22.9–29.8 mg kg^–1, which was still sufficient to satisfy crop growth requirements. Additionally, fertilization cessation increased the proportions of fine colloids (100–450 nm, including nontronite and some amorphous iron oxides) and drove a significant release of iron/aluminum oxide nanoparticles (1–100 nm) and associated P with orthophosphate and pyrophosphate species. In summary, short-term fertilization cessation effectively alleviated soil acidification and inorganic P accumulation, while concomitantly maintaining soil P fertility and improving the potential mobilization of P associated with microparticles.

Phosphorus (P) limitation in the coming decades calls for the utilization of alternative fertilizers in agriculture. Struvite is a promising P source, but its potential role as a fertilizer is dependent on different physical, chemical, and biological properties, which are very heterogeneous in soil, complicating the prediction of the best soil conditions for its application. Here, we evaluated the solubility of struvite in soil, its redistribution into P fractions, and its potential abiotic and biotic drivers in 62 globally distributed soils with contrasting properties through an incubation assay. We found that after 40 d, about 35% of struvite P was redistributed into soil fractions more accessible to plants and microbes. Phosphorus redistribution from struvite was driven by a complex suite of soil physical, chemical, and microbial properties as well as environmental factors that varied across soils. Soil texture played a critical role in determining the redistribution of P in struvite-amended soils in soluble (H₂O extraction), labile (NaHCO₃ extraction), and moderately labile (NaOH extraction) fractions. In addition, the soil solution cation concentration was one of the most important drivers of available struvite-derived P fractions. The great importance of texture and cations in determining struvite-derived P fractions in soil was contrasted with the relatively minor role of pH. At the microbial level, the number of bacterial operational taxonomic units (OTUs) from the unfertilized soils that correlated with struvite-derived P fractions was higher than that of fungi. The number of OTUs that correlated with the struvite-derived soluble P fraction was dominated by fungi, whereas the number of OTUs that correlated with the struvite-derived labile P fraction was dominated by bacteria. Overall, this study provided a predictive framework for the potential use of struvite as a P fertilizer in contrasting soils.