Background: Raising nitrogen use efficiency of crops by improving root system architecture is highly essential not only to reduce costs of agricultural production but also to mitigate climate change. The physiological mechanisms of how biochar affects nitrogen assimilation by crop seedlings have not been well elucidated.Results: Here, we report changes in root system architecture, activities of the key enzymes involved in nitrogen assimilation, and cytokinin (CTK) at the seedling stage of cotton with reduced urea usage and biochar application at different soil layers (0–10 cm and 10–20 cm). Active root absorption area, fresh weight, and nitrogen agronomic efficiency increased significantly when urea usage was reduced by 25% and biochar was applied in the surface soil layer. Glutamine oxoglutarate amino transferase (GOGAT) activity was closely related to the application depth of urea/biochar, and it increased when urea/biochar was applied in the 0–10 cm layer. Glutamic-pyruvic transaminase activity (GPT) increased significantly as well. Nitrate reductase (NR) activity was stimulated by CTK in the very fine roots but inhibited in the fine roots. In addition,AMT1;1, gdh3, andgdh2were significantly up-regulated in the very fine roots when urea usage was reduced by 25% and biochar was applied.Conclusion: Nitrogen assimilation efficiency was significantly affected when urea usage was reduced by 25% and biochar was applied in the surface soil layer at the seedling stage of cotton. The co-expression ofgdh3andgdh2in the fine roots increased nitrogen agronomic efficiency.The synergistic expression of the ammonium transporter gene andgdh3suggests that biochar may be beneficial to amino acid metabolism.

Biomass pyrolysis by-products, such as biochar (BC) and wood vinegar (WV), are widely used as soil conditioners and efficiency enhancers in agriculture. A pot experiment was conducted to examine the effects of WV, both alone and in combination with BC, on soil properties in mildly saline soil and on cotton stress tolerance. The results demonstrated that BC and WV application, either individually or together, increased soil nutrient content. The combined application was more effective than the individual applications, resulting in a 5.18–20.12% increase in organic matter, a 2.65–15.04% increase in hydrolysable nitrogen, a 2.23–58.05% increase in effective phosphorus, and a 2.71–29.38% increase in quick-acting potassium. Additionally, the combined application of WV and BC led to greater improvements in cotton plant height, net photosynthetic rate (Pn), leaf nitrate reductase (NR), superoxide dismutase (SOD), and catalase (CAT) activities compared to the application of BC or WV alone. The enhancements in this study varied across different parameters. Plant height showed an increase of 14.32–21.90%. Net photosynthetic rate improved by 13.56–17.60%. Leaf nitrate reductase increased by 5.47–37.79%. Superoxide dismutase and catalase showed improvements of 5.82–64.95% and 10.36–71.40%, respectively (p < 0.05). Moreover, the combined treatment outperformed the individual applications of WV and BC, resulting in a significant decrease in MDA levels by 2.47–51.72% over the experimental period. This combined treatment ultimately enhanced cotton stress tolerance. Using the entropy weight method to analyze the results, it was concluded that the combined application of WV and BC could enhance soil properties in mildly saline soils, increase cotton resistance, and hold significant potential for widespread application.

Biochar applied to soil has been considered as an effective tool for mitigation of atmospheric carbon dioxide emission and enhancement of carbon storage in soil, which may also enhance soil quality. However, the effect of biochar aged for 5 years on the different carbon fractions and enzyme activities as well as its changes, is not well understood in the cropland sandy soil of northern China. Therefore, a field trial was carried out in 2014 with biochar applied once at 0, 5.25, 10.50, 21.00 and 42.00 g·kg⁻¹ (BC0, BC1, BC2, BC3, and BC4, respectively). We evaluated the influence of biochar addition to the changes in soil organic carbon (SOC), labile carbon pools (readily oxidized carbon, dissolved organic carbon, and microbial biomass carbon) and enzyme activities (invertase, urease, and catalase). Biochar significantly increased SOC (122.00%) and altered the content of labile carbon (increased ROC, DOC and MBC by 71.29%, 10.35%, and 900.00%, respectively). Soil urease and invertase activities increased by 55.81% and 46.76%, respectively, with an increase in biochar application rate, but catalase activity significantly decreased by 31.79%. The values of the geometric means of labile carbon (0.88) and enzyme activities (2.39) for the BC3 treatment were higher than others, which indicated that the biochar application rate of 21.00 g·kg⁻¹ is suggested for the sandy soil. Our results suggest that the application of biochar in sandy soil for five years increased soil carbon sequestration, changed enzyme activities and ameliorated soil quality.

Drought and salt stresses are critical environmental constraints affecting plant growth and development, and microorganisms can enhance plant tolerance to these abiotic stresses through complex mechanisms. This review systematically synthesizes the core mechanisms by which microorganisms regulate plant physiological and biochemical processes under such stresses, specifically including the following: (1) regulating the perception and transduction of abiotic stress signals to enhance plant adaptive responses; (2) boosting gene expression and protein synthesis for overall plant metabolic regulation; (3) activating the antioxidant system to strengthen plant tolerance; (4) modulating plant hormone levels to stimulate growth in response to adversity; (5) enhancing plant nutrition and absorption to improve resilience; (6) optimizing the photosynthesis system to promote the synthesis of essential substances, safeguarding plant growth and development amidst adversity. Finally, the application of microbial inoculants in saline–alkali soil improvement and crop cultivation in arid areas and prospective research directions are discussed.

As a good carbon source and soil conditioner, biochar is widely used in acidic soils but seldom in alkaline soils due to its high pH. In this study, cotton straw biochar was modified with five different acidic materials to obtain wood-vinegar- (WBC), monosodium-glutamate (MSG)-wastewater- (MBC), citric-acid- (CBC), phosphoric-acid- (PBC), and nitric-acid-modified biochars (NBC), and three dosages were used for each modifier. The pristine and modified biochars were characterized with scanning electron microscopy (SEM) and Fourier-transform infrared (FTIR) spectroscopy. The biochar properties such as pH, specific surface area (SSA), and elemental contents were measured. In addition, the technique for order preference by similarity to ideal solution (TOPSIS) model based on entropy weight was used to evaluate the application potential of the biochars in alkaline soils. The FTIR spectra showed that modification with the five acidic materials, MSG wastewater in particular, resulted in more oxygen-containing functional groups such as O-H, C=O, and C-O on the biochar surface. In addition, acid modification greatly decreased the pH: phosphoric acid modification significantly decreased the pH of cotton straw biochar by 5.71–7.88 units. For the same modifier, a higher dosage (i.e., a smaller biochar:modifier ratio) led to a larger decrease in the pH of cotton straw biochar. The magnitudes of increase in total soluble salt content followed the general order of CBCs > PBCs > WBCs > NBCs > MBCs. The SSA, average pore diameter, and total pore volume of biochar were changed as well. Modification using wood vinegar and MSG wastewater significantly decreased the SSA of cotton straw biochar by 15.58–16.24 m² g⁻¹ (82.7–86.2%) and 15.87–16.80 m² g⁻¹ (84.2–89.2%), respectively, whereas modification using citric acid and nitric acid significantly increased the SSA of cotton straw biochar by 4.51–4.66 m² g⁻¹ (23.9–24.7%) and 0.55–54.21 m² g⁻¹ (2.9–287.7%). The evaluation based on entropy weight TOPSIS model suggested that the MBCs have the highest potential for application in alkaline soils. This study presents a theoretical basis for evaluation of biochar application potential, demonstrates a way of improving biochar application potential, and provides a support for beneficial utilization of agricultural and industrial wastes such as cotton straw, wood vinegar, and MSG wastewater.

To evaluate the effects of saline water on the yield and quality of tomatoes, a late fruit-setting stage irrigation experiment was conducted in a greenhouse using two cultivars: medium-fruited, tasty Strawberry tomato (fresh-eating) and large-fruited Maofen tomato (fresh/processing). For this, plants were grown in pots containing substrate, and five irrigation water electrical conductivity (EC) levels (1.0 as control, 2.6, 4.2, 5.8, and 7.4 dS m⁻¹) were applied for each cultivar, resulting in a 2 × 5 factorial design with 10 treatments in total. Then, tomato growth, fruit ion composition, and quality attributes were evaluated. The results showed that 1.0–7.4 dS m⁻¹ saline water had no significant impact on the plant height, stem diameter, single-fruit weight, or total yield of either cultivar. However, Strawberry tomato’s marketable yield decreased by 23.5% at 7.4 dS m⁻¹. The yield per plant of Maofen tomato was 2.7 times that of Strawberry tomato. Fruit Na⁺ content increased with EC for both cultivars; Maofen tomato had higher Na⁺ and a lower K⁺/Na⁺ ratio, with greater ion content responses to salinity. Regression analysis revealed distinctly nonlinear responses in key yield, ion, and quality parameters across the salinity gradient. The fruit comprehensive quality score (CQS) rose with EC, and Strawberry tomato’s average CQS increase (109%) was significantly higher than Maofen tomato’s. In conclusion, saline irrigation initiated when the fourth-cluster fruits attained 60% of the final harvested diameter, at EC ≤ 5.8 dS m⁻¹ for Strawberry tomato and ≤7.4 dS m⁻¹ for Maofen tomato, improved fruit quality without compromising yield. Strawberry tomato is recommended for quality-oriented production, whereas Maofen tomato is better suited for yield-oriented production, providing scientific support for saline water utilization in greenhouse soil-less cultivation.