Application of the organic fertilizers can improve soil properties and agricultural product quality, while the in-depth effect of organic fertilizer needs further exploration. In this study, the apple fruit (Malus pumila Mill.) quality, soil physicochemical characteristics, and microbial community under different fertilizers including control without fertilizer (CK), composted manure (CM), biogas slurry (BS), and chemical fertilizer (CF) were systematically investigated, and each treatment was repeated three times in completely random block plots with equal NPK content of fertilizer applied in each treatment. The CM treated apple fruit were observed with the best vertical diameter (78.72 ± 4.32 mm), transverse diameter (87.51 ± 1.3 mm), and color index (L* = 55.48 ± 5.48, b* = 18.96 ± 1.86). Meanwhile, the CM and BS treated apple fruit had higher flesh firmness than that of CK and CF treatment, implying that the organic fertilization can improve the storability and crispy taste apple fruit. Furthermore, the total sugars, essential amino acid, crude protein, total acids, and soluble solid contents of apple fruit were also significantly improved by using CM and BS fertilizer due to the resulting higher N, P, and organics content in soil. The application of organic fertilizer also dramatically enhanced the bacterial and fungi diversity, which may contribute to better soil respiration. The results obtained in this study reveals the insight effect of organic fertilizer on improvement of fruit quality and soil health and can supply technical assistance to organic cultivation of apple.

When carbon quantum dots (CDs) are used to enhance photosynthesis, they inevitably enter the plant. However, the dose-dependent effects of CDs on plant growth are poorly understood. In this study, we investigated the dose-dependent effects of CDs on soybean growth. CDs were synthesized from citric acid and urea via a hydrothermal procedure. The analysis of the structure, chemical composition, and optical properties revealed that synthetic CDs have a sphere-like shape with rich hydrophilic groups on their surface. CDs exhibited superior upconverted photoluminescence properties and emitted strong fluorescence (exciting wavelength of 220 nm; emitting wavelength of 438 nm). Various concentrations of synthetic CDs (0–1000 mg L⁻¹), as a photosynthesis enhancer, were applied to soybean plants under hydroculture for 1–10 days. CDs positively affected soybean growth at concentrations less than 200 mg L⁻¹. However, at higher concentrations (500 or 1000 mg L⁻¹), they exhibited significant toxicity to plant growth, which was evidenced by the mass accumulation of CDs in damaged leaves. Metabolomic and transcriptomic analyses indicated that CDs at a low concentration (100 mg L⁻¹) could increase antioxidant and biomass accumulation in soybeans to promote plant growth. This study provided valuable insights into the impacts of CDs on plants in sustainable agricultural practices involving the use of nanomaterials.