Earthworms and Arbuscular Mycorrhizal Fungi Alleviated Salt Stress in Maize Seedlings by Regulating the Root Endodermis Diffusion Barrier

Under salt stress, the root system is the first barrier in plant resistance. Endodermal suberin in plant roots can act as a diffusion barrier to effectively control ion uptake under abiotic stress. Soil biological interaction can affect plant root anatomic characters. In this study, the effects of earthworms (Eisenia foetida) and arbuscular mycorrhizal (AM) fungi (Funneliformis mosseae) on the maize root diffusion barrier in saline-alkali soil and the distribution characteristics of Na+ were investigated. Maize seedlings grown in soil amended with earthworms and AM fungus were measured, and FY088 fluorescence staining was used to locate the accumulation of suberin in the endodermis. Scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDS) scanning was used to analyze the distribution of Na+ in the cross-section of roots, and inductively coupled plasma-optical emission spectrometry (ICP-OES) was used to measure the mineral absorption of plants. The results showed that the total biomass of maize seedlings under salt stress increased by 70.4% with the amendment of earthworms and AM fungus, compared with the group without the amendment. Earthworms and AM fungus significantly changed the root anatomy of maize seedlings in saline-alkali soil increasing the accumulation of suberin layers in maize endodermis, effectively changing the distribution characteristics of Na+ in root cross-section, reducing the transfer of Na+ to stele, and increasing the K/Na ratio in roots and shoots by 59.8% and 73.3%, respectively. Our research showed that in saline-alkali soil, earthworms and AM fungus mediated root development and anatomical structure changes of maize, which was beneficial to maintain ion homeostasis of maize seedlings and improve root salt tolerance. This study provides new evidence for earthworm-mycorrhizal interaction to improve plant salt tolerance in saline-alkali soil.