Phosphorous and Arbuscular Mycorrhizal Fungi Improve Snapdragon Flowering Through Regulating Root Architecture and Phosphorus Nutrition

Snapdragon (Antirrhinum majus L.) is a popular ornamental plant, but its growth and flowering can be limited by inadequate soil phosphorus (P) availability. Arbuscular mycorrhizal fungi (AMF) can form symbiotic associations with plants and enhance their P uptake and growth. This study investigated the effects of varying P levels (0, 0.05, 0.1, 0.2, and 0.4 mM KH2PO4 solution) and AMF inoculation (mixture of Funneliformis mosseae and Glomus versiforme) on the P uptake, growth, and flowering of snapdragon. The results showed that P addition improved snapdragon root traits to different degrees and prolonged flowering time from 1 to 5 days. P addition generally reduced most of the organic acid contents. AMF inoculation with or without P addition improved root traits, among which 0.1 mM P + AMF inoculation showed the highest mycorrhizal colonisation percentage. It promoted the activities of phosphoenolpyruvate carboxylase and acid phosphatase in roots, and P uptake compared with the 0.1 mM P treatment and the control. Moreover, it increased the inflorescence length, flower density, and corolla diameter of the floret and prolonged the flowering duration to 22 days, 4-10 days longer than other treatments. The results suggest that combining P fertilisation with AMF inoculation was the most effective approach in improving root traits and P nutrition and increasing the number of flowers, flower quality, and flowering duration of snapdragons.