LAUSR

Abstract Arizona cypress is a major urban landscape tree many of which have declined in the recent years. Although the cause for this decline is complicated, drought is generally thought to be a leading factor. This study was designed to investigate the effects of artificial inoculation of seedlings of a major urban forest tree, Arizona cypress (Cupressus arizonica Green) with beneficial microorganisms under the water stress. We conducted this research with three factors comprising arbuscular mycorrhizal fungi (AMF) inoculation with Rhizophagus irregularis or Funneliformis mosseae or a combination of the both fungi species (CF), bacterial inoculation with Pseudomonas fluorescens (PF) and non-inoculated controls, and two levels of irrigation including well-watered (WW) and severe-water deficiency (SWD) using three replications of each treatment. The results clearly showed that SWD adversely affected root colonization, morphological parameters, relative water content, and soluble carbohydrate content. However, antioxidant enzyme contents (i.e. catalase, superoxide dismutase, glutathione peroxidase, ascorbate peroxidase), hydrogen peroxide, malondialdehyde, and proline increased as a result of water stress. Moreover, AMF-inoculated plants grew better than non-inoculated plants under SWD conditions. Dual-inoculated plants with CF and PF inoculation accumulated more ascorbate peroxidase and glutathione peroxidase than plants with merely PF or AMF inoculation under SWD conditions. Inoculated plants significantly decreased the water deficit-induced hydrogen peroxide and malondialdehyde in Arizona cypress leaves. In conclusion, the symbiotic association between PF and AMF can alleviate water-deficit damage and improve water stress tolerance in the Arizona cypress.