Enhancement of photosynthetic parameters and growth of Zelkova serrata by arbuscular mycorrhizal fungi under simulated sulfuric acid rain

Acid rain (AR) is a frequent environmental issue in southern China that causes damage to the growth and photosystems of subtropical tree species. Arbuscular mycorrhizal fungi (AMF) can improve plant tolerance to acidic conditions; however, how AMF mediate the detrimental effects of AR on the growth and photosynthetic parameters of tree species is yet to be understood. In this study, we inoculated Zelkova serrata, an important economic tree species in China, with Rhizophagus irregularis, and Diversispora versiformis, alone and in combination, under three simulated AR regimes (pH 2.5, 4.0, and 5.6). Mycorrhizal colonization, the concentrations of succinate dehydrogenase (SDH) and alkaline phosphatase (ALP) in hyphae, leaf chlorophyll fluorescence and photosynthetic parameters, and growth were all subsequently measured. Our results revealed that AR sharply reduced photosynthetic ability and total biomass of non-mycorrhizal plants, whereas AMF inoculation significantly improved ALP, SDH, total biomass, net photosynthetic rate, and acid tolerance under acidic conditions compared to the non-mycorrhizal controls. Moreover, the acid tolerance of Z. serrata was positively correlated with net photosynthetic rate. Furthermore, our results indicated that mycorrhizal efficiencies varied with the intensity of AR and AMF identities, with D. versiformis proving much more efficient than the other fungi under acidic conditions. Overall, our findings highlight the significance of AMF associations for tree species suffering from AR stress and provide insight into strategies for improving the acid tolerance of plants.