Effects of arbuscular mycorrhizal fungi on the adaptability of Sophora davidii under low phosphorus stress

The lack of phosphorus in the soil is one of the important factors restricting the healthy growth of Sophora davidii in karst areas, and improving the absorption of phosphorus is of great significance to the growth and utilization of S. davidii . Arbuscular mycorrhizal fungi (AMF) can form a mutualistic symbiotic relationship with plants, which can relieve stress and promote the growth of host plants. A sand culture method was used in this study. S. davidii seedlings inoculated with AMF and without AMF (NAM) were used as research materials under three phosphatase treatments, P0.5 (0.5 mmol/L), P0.25 (0.25 mmol/L), and P0 (0 mmol/L), to investigate the effects of arbuscular mycorrhizal fungi on the growth, morphology, physiology, endogenous hormone contents and accumulation of N and P elements in S. davidii seedlings. The results showed that under NAM, the plant height, growth rate, aboveground dry weight and chlorophyll content were significantly decreased under low phosphorus stress. Under low phosphorus stress (P0.25) intensity, S. davidii showed increased root dry weight, root shoot ratio, total root length, root surface area, root tip number, and root hair number, an increased content of osmotic adjustment substances such as proline, soluble sugar and soluble protein, increased activity of protective enzymes such as acid phosphatase and catalase, and increased hormone contents to adapt to the low phosphorus stress. However, when the low phosphorus stress intensity increased to P0, the regulatory effect was severely weakened. Inoculation with AMF promoted the growth of the aboveground parts of S. davidii ; although it decreased the growth of the root system and root biomass, it significantly increased the total root length, root tip number and growth rate under P0 stress and increased chlorophyll a, total chlorophyll, proline, soluble sugar, soluble protein, and IAA contents, and acid phosphatase and superoxide dismutase activities. The roots of S. davidii and AMF engage in symbiosis, improving root morphology, promoting the absorption of nitrogen and phosphorus by seedlings, and maintaining the N:P balance of leaves, thereby maintaining a higher biomass of S. davidii under low phosphorus stress and relieving the low phosphorus stress on seedlings. Our results demonstrated that AMF inoculation is useful for the promotion and cultivation of S. davidii in the karst area of Southwest China under low phosphorus stress conditions. Therefore, in the process of ecological restoration and forage improvement using S. davidii on acidic soil in the karst region of Southwest China, inoculation with AMF may be a good strategy to stabilize S. davidii yields.