Biochar alleviated the salt stress of induced saline paddy soil and improved the biochemical characteristics of rice seedlings differing in salt tolerance

Biochar is used mainly to alleviate salt stress in arid and semiarid soils, or to regulate acidification stress in paddy soils. However, the effects of biochar on paddy soil environments under salt stress and the biochemical characteristics of rice seedlings differing in salt tolerance are unclear. This study explored whether and how biochar is involved in alleviating salt stress in paddy soil and regulating the biochemical characteristics of rice seedlings. The trial was conducted under pot culture conditions, and NaCl was used as the salt stress agent in paddy soil. Two rice varieties were used in this trial: Jinyuan 85 (a salt-tolerant rice variety) and Nipponbare (a salt-sensitive rice variety). The salt stress included three treatments: 0 g NaCl kg−1 dry soil (control, S0), 1 g NaCl kg−1 dry soil (S1), and 3 g NaCl kg−1 dry soil (S3). Biochar produced by rice straw involved three treatments: no biochar (control, C0), biochar produced at 300℃ applied into soil (C300), and biochar produced at 600℃ applied into soil (C600). The results suggested that the adsorption ability of the biochar produced at 600℃ was significantly higher than that of the biochar produced at 300℃. Bulk density, electrical conductivity, exchangeable Na+ and exchangeable Cl- in the soil under salt stress were greatly decreased by the application of biochar, and the soil environment of C600 was more favorable for rice seedlings. The salt accumulations in the rice seedling, and the microstructure of the root and leaf of the rice seedlings under salt stress were significantly and positively affected by the biochar, and the biochemical characteristics of the rice seedlings also greatly improved in response to biochar application. The responses of Nipponbare to salt stress were more severe than those of Jinyuan 85, while the regulatory effects of biochar were more favorable for Jinyuan 85 than for Nipponbare. In conclusion, biochar, especially that produced at 600℃ in this trial played a positive role in alleviating the inhibitory effects of salt stress on rice seedlings, and might be useful as an amendment in saline soils to improve rice plant growth.