The impact of arbuscular mycorrhizal fungi on soybean growth strategies in response to salt stress

Aims: Salt stress presents a significant impediment to crop growth and development. However, the effects of indigenous arbuscular mycorrhizal fungi (AMF) and the addition of exogenous AMF on soybean growth strategies under salt stress remain poorly understood. The purpose of this study was to examine the impact of different AMF sources on soybean growth strategies under salt stress conditions. Methods: In this study, we established three different salt stress gradients (1, 2, and 4 g NaCl kg⁻¹ soil) along with two AMF treatments (indigenous AMF and added exogenous AMF) to evaluate soybean growth parameters, enzymes, and soil indicators. Results: Under salt stress, exogenous AMF significantly increased mycorrhizal colonization in soybean, resulting in a notable enhancement in phosphorus (P) and potassium (K) concentration while reducing nitrogen (N) absorption. Additionally, the addition of exogenous AMF demonstrated the capacity to enhance soybean salt tolerance by lowering soybean sodium (Na) and malondialdehyde (MDA) content, catalase (CAT) activity, and increasing K⁺/Na⁺ ratio and acid phosphatase (A-Pase) activity. In contrast, in the indigenous AMF treatment, rhizosphere A-Pase activity in soybean exhibited predominantly positive correlations with each trait, and the K⁺/Na⁺ ratio relied more on mycorrhizal colonization and CAT activity. Soybean biomass was influenced both directly and indirectly, with the K⁺/Na⁺ ratio serving as a crucial pivot in the indirect pathway. Conclusions: The addition of exogenous AMF can enhance soybean salt tolerance by regulating nutrient and sodium absorption, enzyme activity, and MDA content. Meanwhile, indigenous AMF promotes salt tolerance in soybeans by global regulating trait associations.