Response of growth and physiological indexes of Helianthus tuberosus to biochar under salt stress

This study aimed to investigate the response mechanism of Helianthus tuberosus to different concentrations of salt stress at the early stage and reveal the short-term effects of biochar on the osmoregulatory effect and antioxidant system of Helianthus tuberosus at different concentrations at the early stage of salt stress. In this study, the following eight treatments were used: no salt stress blank control (CK), 1.67 g·kg⁻¹ salt stress (Y₁), 3.35 g·kg⁻¹ salt stress (Y₂), 5.02 g·kg⁻¹ salt stress (Y₃), no salt stress + 5% biochar (S₀), 1.67 g·kg⁻¹ salt stress + 5% biochar (S₁), 3.35 g·kg⁻¹ salt stress + 5% biochar (S₂), and 5.02 g·kg⁻¹ salt stress (S₃). The effects of different concentrations of biochar additions at the early stage of salt stress on plant height, ground diameter, osmoregulatory substance content, malondialdehyde content, and antioxidant enzyme activities of Helianthus tuberosus were analyzed. The results showed that 1) Helianthus tuberosus could grow normally within the range of 0～1.67 g·kg⁻¹ soil salt content, and when the soil salt content exceeded 3.35 g·kg⁻¹, salt stress occurred, which significantly inhibited the growth of Helianthus tuberosus (P < 0.05). Furthermore, the content of osmoregulatory substances such as soluble protein (SP), soluble sugar (SS), proline (Pro), and malondialdehyde (MDA) increased significantly (P < 0.05), and antioxidant enzyme activities such as peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) were significantly increased (P < 0.05). 2) Biochar effectively improved the resistance of chicory to salt stress, significantly reduced malondialdehyde content, and alleviated the growth inhibition of chicory by salt stress, in which, compared to 5.02 g·kg⁻¹ salt stress, the increment of SP, SS, and Pro decreased by 161.76%, 16.83%, and 55.48%, respectively, and the increment of MDA decreased by 61.83%. In addition, the POD, SOD, and CAT activities were also reduced by 71.85%, 66.25%, and 340.05%, respectively. Therefore, the addition of biochar can effectively alleviate membrane lipid peroxidation caused by salt stress, improve antioxidant capacity, and enhance the resistance of jicama to salt stress.