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

Abstract

Abstract 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 mechanisms by which AMF protect Zelkova serrata, an economically important tree species in southern China, from AR stress remain unclear. We conducted a greenhouse experiment in which Z. serrata plants were inoculated with AMF species Rhizophagus intraradices and 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 AR and nitric AR (pH 2.5, 4.0 and 5.6) to examine any interactive effects on growth, photosynthetic capabilities, antioxidant enzymes, osmotic adjustment and soil enzymes. 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, peroxidase, superoxide dismutase, SP and root acid phosphatase activity of Z. serrata under harsh AR stress. Moreover, the benefits from AMF symbionts depended on the identity of AM fungal species and the gradient of AR stress. Our results indicate that AM fungi protect Z. serrata against AR stress by synchronously activating photosynthetic ability, antioxidant enzymes and osmolyte accumulation. These findings suggest that a combination of R. intraradices and D. versiformis may be a preferable choice for culturing Z. serrata in southern China.