Besides biomass production, some microalgae have been used to treat wastewater contamination. However, in general, high concentrations of heavy metals significantly inhibit algal growth. We thus need to find ways to promote the resistance of microalgae to heavy metals, increase their growth rate under stress, and achieve coupling of heavy metal removal and biomass production simultaneously. In this review, mechanisms for removal of heavy metals by microalgae are proposed. Effects of exogenous chemical additives (dissolved organic matters, formaldehyde, sulphate, phosphate, nitric oxide donors, etc.) on algal biosorption to heavy metals are summarized. Genetic manipulation and microalgal strain selection strategies are also introduced, especially for the acid-tolerant strains with high biosorption efficiencies to Cr(VI) and Cd²⁺ at low pH conditions. Recent advances in (semi)continuous heavy-metal-bioremediation and biomass-production coupled system with immobilized microalgae, as well as challenges and solutions to the commercialization and industrialization of the coupled system were discussed.

The intensive use of chemical fertilizers in China to maintain high crop yields has led to significant environmental degradation and destabilized crop production. Returning straw to soil presents a potential alternative to reduce chemical fertilizer requirements and enhance soil fertility. This study investigates the effects of different nitrogen (N) input levels and straw additions on crop phosphorus (P) uptake and soil P availability based on a long-term N-fertilizer trial. The treatments included no fertilizer input (CK), conventional (NPK), reduced NPK (0.75NPK), and straw-amended (SNPK) treatments. Results indicate that SNPK significantly enhances shoot P uptake and crop yields by 43.7–61.9% and 29.3–39.6%, respectively. The SNPK treatment improved rhizosphere P availability and increased the phosphorus activation coefficient (PAC) by 1.72-fold compared to NPK alone. The enhanced soil P availability under SNPK was primarily attributed to an abundance of functional microbes, leading to higher P storage in the microbial biomass P pool and its turnover. Additionally, SNPK promoted root exudate and phosphate-mobilizing microbes, enhancing P mobilization and uptake. Nitrogen fertilization primarily influenced root functional traits related to P acquisition. These findings provide valuable insights for developing effective fertilizer management strategies in maize–oilseed rape rotation systems, emphasizing the benefits of integrating straw with chemical fertilizers.

Exogenous carbon addition is widely regarded as an effective soil management strategy for rapidly increasing soil organic carbon, improving soil structure and function. However, a systematic comparison of the effects of diverse organic amendments on key soil attributes and processes is needed to inform their targeted application. We evaluated the impacts of seven organic amendments (biochar, organic fertilizer, corn straw, soybean straw, rapeseed straw, green manure, and carbon material) on a purple soil (Luvic Xerosols) in a pot experiment. The results showed that organic fertilizer and carbon material performed best in enhancing soil nutrient availability and promoting soil organic carbon content. Straw amendments promoted the formation of macro-aggregates. Green manure and straws enhanced carbon transformation-related β-glucosidase and cellobiohydrolase activities. Random Forest and structural equation modeling indicated that the organic amendments enhanced maize carbon sequestration capacity and biomass by improving aggregate stability and regulating the fungal community and by increasing nutrients and enhancing active carbon fractions. Green manure and organic fertilizer demonstrated the most significant agronomic effects. These findings provide guidelines for targeted organic amendment selection in purple soil regions.

Biochar is an effective method for increasing soil carbon (C) sequestration and nitrogen (N) supply under continuous monocropping. To investigate the impact of biochar placement methods on soil C and N, a one-year field experiment with five treatments was conducted including control, mineral fertilizers only (F), biochar hole placement (BFH; biochar applied to the soil layer at 5–10 cm) + F, biochar band placement (BFB; biochar applied to the soil layer at 15–20 cm) + F, and biochar band and hole placement + F (BFBH). The results showed that, regardless of the placement method, biochar application increased soil total organic C (TOC) and C pool management index by 6.9–39.7% and 4.1–36.1%, respectively, especially for dissolved organic C (DOC; 6.9–51.3%), readily oxidizable C (ROC; 2.4–46.4%), and microbial biomass C (MBC; 10.4–41.7%). Single biochar placement methods significantly influenced DOC, MBC, and ROC contents of both soil layers in the rank order of BFH ≈ BFBH > BFB at 0–15 cm and BFB ≈ BFBH > BFH at 15–30 cm. Soil TN and microbial biomass N (MBN) mainly accumulated at the site of biochar placement. The increased soil TOC:TN and MBC:N ratios under biochar treatments promoted inorganic N immobilization and reduced the loss of ammonium N and nitrate N (NO₃⁻-N) through leaching at the early stage of tobacco growth. Biochar-adsorbed N was remobilized at a later period (vigorous growth stage and maturity), possibly causing the slow decrease in NO₃⁻-N content. Additionally, soil C and N pools were significantly influenced by the main effects of soil layer and growth stage. Overall, biochar application increased soil C and N pools and inorganic N supply through N remobilization. However, the increased labile organic C content and microbial activity may prevent C sequestration in biochar-amended soils.

Nitrogen (N) stress seriously constrains barley (Hordeum vulgare L.) production globally by influencing its growth and development. In this study, we used a recombinant inbred line (RIL) population of 121 crosses between the variety Baudin and the wild barley accession CN4027 to detect QTL for 27 traits at the seedling stage in hydroponic culture trials and 12 traits at the maturity stage in field trials both under two N treatments, aiming to uncover favorable alleles for N tolerance in wild barley. In total, eight stable QTL and seven QTL clusters were detected. Among them, the stable QTL Qtgw.sau-2H located in a 0.46 cM interval on the chromosome arm 2HL was a novel QTL specific for low N. Notably, Clusters C4 and C7 contained QTL for traits at both the seedling and maturity stages. In addition, four stable QTLs in Cluster C4 were identified. Furthermore, a gene (HORVU2Hr1G080990.1) related to grain protein in the interval of Qtgw.sau-2H was predicted. Correlation analysis and QTL mapping showed that different N treatments significantly affected agronomic and physiological traits at the seedling and maturity stages. These results provide valuable information for understanding N tolerance as well as breeding and utilizing the loci of interest in barley.