Application of AMF Alleviates Growth and Physiological Characteristics of Impatiens walleriana under Sub-Low Temperature

Impatiens walleriana is of great ornamental value, but it may suffer growth inhibition when it is exposed to sub-low temperatures for a long time. Although there are many studies on the positive effect of arbuscular mycorrhizal fungi (AMF) on cold tolerance, whether AMF could alleviate the sub-low temperature injury of Impatiens walleriana is unknown. In this experiment, two kinds of Impatiens walleriana were inoculated with AMF and treated with sub-low temperature to evaluate the physiological and biochemical characteristics of Impatiens walleriana seedlings. The results showed that the plant height of ‘Super Elf (Rose red)’ under stress and inoculated with 50 g and 100 g AMF compared to sub-low temperature treatment increased by 4.94% and 19.01%, and the plant height of ‘Super Elf (red)’ under stress and inoculated with 50 g and 100 g AMF increased by 3.11% and 17.03%, respectively. Compared to sub-low temperature treatment, the stem diameter of ‘Super Elf (Rose red)’ under stress and inoculated with 50 g and 100g AMF increased by 47.17% and 50.94%, respectively. The same mitigation effect was observed in ‘Super Elf (red)’. Compared with sub-low temperature treatment, Fv’/Fm’, Y(II) and qP of ‘Super Elf (Rose red)’ inoculated with 50 g AMF significantly increased by 75.76%, 52.17%, and 43.48%, while NPQ significantly decreased by 2.96 times, whereas the corresponding values for ‘Super Elf (Rose red)’ inoculated with 100 g AMF increased by 87.88%, 82.61%, and 65.22%, while NPQ significantly increased by 1.47 times. Compared with sub-low temperature treatment, Fv’/Fm’, Y(II) and qP of ‘Super Elf (red)’ inoculated with 50 g AMF significantly increased by 53.49%, 28.95%, and 29.31%, while NPQ significantly decreased by 0.84 times, whereas the corresponding values for ‘Super Elf (red)’ inoculated with 100 g AMF increased by 53.49%, 23.68%, and 22.41%, while NPQ significantly increased by 3.48 times. Meanwhile, ‘Super Elf (Rose red)’ and ‘Super Elf (red)’ vaccination with AMF reduced the levels of O2− and H2O2 accumulation in leaves at sub-low temperatures and mitigated the extent of damage to cell membrane lipid peroxidation. Therefore, AMF inoculation can improve the tolerance of plants to sub-low temperatures.