Arbuscular mycorrhizal fungi protect a subtropical tree species exposed to simulated acid rain by accelerating photosynthetic ability, antioxidant enzymes and osmolyte accumulation

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.