Acid rain (AR) is an increasingly serious environmental problem that frequently occurs in Southern China with sulfuric acid rain (SAR) as the main type. SAR can negatively affect the growth and physiological properties of trees, but mycorrhizal associations may mitigate such detrimental effects. However, the mechanisms by which arbuscular mycorrhizal fungi control SAR-induced impacts on Torreya grandis plants remain unclear. A pot experiment was conducted on T. grandis seedlings, an economically important tree species in Southern China, in which inoculated and non-inoculated T. grandis seedlings were subjected to three simulated SAR regimes (pH of 5.6, 4.0, and 2.5, respectively) to examine the effects on the growth, osmotic regulation, and nutrient absorption of these seedlings. The results show that, although SAR had no effect on the accumulation of biomass, it significantly decreased the concentrations of proline and soluble protein, shoot Zn2+, P, K+, and Ca2+ concentrations, and the Fe2+ and Mn2+ concentrations of shoots and roots. Mycorrhizal inoculation, especially with Rhizophagus irregularis, significantly increased total biomass, proline concentration, and the Zn2+, P, and K+ concentrations in the shoots of T. grandis under lower pH conditions. Moreover, our findings suggest that the combination of root colonization, acid tolerance, and the concentrations of shoot-P, shoot-Zn2+, and root-Fe2+ of T. grandis jointly conferred mycorrhizal benefits on the plants under SAR conditions. Given the enhancement of the nutritional quality of T. grandis owing to mycorrhizal associations, inoculation with R. irregularis may be preferable for the culturing and management of these plants under acidic conditions.

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Aims acid rain (AR), which occurs frequently in southern China, negatively affects the growth of subtropical tree species. Arbuscular mycorrhizal fungi (AMF) mitigate the detrimental effects induced by AR. However, the mechanism by which AMF protects Zelkova serrata, an economically important tree species in southern China, from AR stress remains unclear. Methods we conducted a greenhouse experiment in which Z. serrata plants that were inoculated with AMF species Rhizophagus intraradices, Diversispora versiformis, either alone or as a mixed culture, or with a sterilized inoculum (negative control). The plants were subjected to three levels of simulated sulfuric and nitric acid rain (pH 2.5, 4.0, and 5.6) to examine any interactive effects on growth, photosynthetic capabilities, antioxidant enzymes, osmotic adjustment and soil enzymes. Important Findings AR significantly decreased dry weight, chlorophyll content, net photosynthetic rate and soluble protein (SP) of non-mycorrhizal plants. Mycorrhizal inoculation, especially a combination of R. intraradices and D. versiformis, notably improved dry weight, photosynthetic capabilities, catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), SP, and root acid phosphatase activity (RAPA) of Z. serrata under harsh AR stress. Moreover, the benefits from AMF symbionts depend on the identity of AM fungal species and the gradient of AR stress. Our results indicated that AM fungi protect Z. serrata against AR stress by synchronously activating photosynthetic ability, antioxidant enzymes, and osmolyte accumulation. The findings of the current study suggest that a combination of R. intraradices and D. versiformis may be a preferable choice for culturing Z. serrata in southern China.