Arbuscular mycorrhizal fungi combined with exogenous calcium improves the growth of peanut (Arachis hypogaea L.) seedlings under continuous cropping

The growth and yield of peanut are negatively affected by continuous cropping. Arbuscular mycorrhizal fungi (AMF) and calcium ions (Ca²⁺) have been used to improve stress resistance in other plants, but little is known about their roles in peanut seedling growth under continuous cropping. This study investigated the possible roles of the AMF Glomus mosseae combined with exogenous Ca²⁺ in improving the physiological responses of peanut seedlings under continuous cropping. G. mosseae combined with exogenous Ca²⁺ can enhance plant biomass, Ca²⁺ level, and total chlorophyll content. Under exogenous Ca²⁺ application, the F_v/F_m in arbuscular mycorrhizal (AM) plant leaves was higher than that in the control plants when they were exposed to high irradiance levels. The peroxidase, superoxide dismutase, and catalase activities in AM plant leaves also reached their maximums, and accordingly, the malondialdehyde content was the lowest compared to other treatments. Additionally, root activity, and content of total phenolics and flavonoids were significantly increased in AM plant roots treated by Ca²⁺ compared to either G. mosseae inoculation or Ca²⁺ treatment alone. Transcription levels of AhCaM, AhCDPK, AhRAM1, and AhRAM2 were significantly improved in AM plant roots under exogenous Ca²⁺ treatment. This implied that exogenous Ca²⁺ might be involved in the regulation of G. mosseae colonization of peanut plants, and in turn, AM symbiosis might activate the Ca²⁺ signal transduction pathway. The combination of AMF and Ca²⁺ benefitted plant growth and development under continuous cropping, suggesting that it is a promising method to cope with the stress caused by continuous cropping.