Harnessing Arbuscular Mycorrhizal Symbiosis to Enhance Growth and Resilience to Combined Drought and Heat Stress in Lily (Lilium spp.)

Abiotic stresses such as drought and heat increasingly threaten plant growth and ornamental quality, particularly in climate-sensitive floricultural crops. Arbuscular mycorrhizal fungi (AMF) are known to enhance plant resilience under such conditions, yet their role in lilies remains insufficiently explored. In this study, we used a two-tier experimental approach to evaluate AMF-mediated benefits in lilies. First, different AMF strains, namely <i>Funneliformis mosseae</i> (FM), <i>Rhizophagus intraradices</i> (RI), <i>Rhizophagus irregularis</i> (RIG), <i>Claroideoglomus etunicatum</i> (CE), <i>Diversispora versiformis</i> (DV), and a mixed consortium (MIX), were screened for growth-promoting effects in two Lilium species, Taiwan lily and <i>Lilium</i> cv. Sorbonne, under non-stress conditions. Second, a selected AMF-host combination from the screening was evaluated to improve tolerance to drought, heat, and combined drought + heat stress. Among the tested strains, DV and MIX showed the most consistent improvements across key growth traits and root colonization. In the stress experiment, stress treatments reduced growth and physiological performance, particularly under combined drought + heat. AMF inoculation enhanced plant performance by improving shoot and root biomass, improving root system architecture, and leading to a higher chlorophyll content, greater relative water content, and enhanced flower traits. Biochemical analyses further revealed that AMF mitigated stress-induced oxidative damage by reducing reactive oxygen species (ROS) accumulation, as shown by reduced O₂•^- and H₂O₂ staining. This reduction in oxidative stress was supported by increased activities of key antioxidant enzymes, indicating that AMF activate cellular defense mechanisms. These findings underscore the potential of AMF as a sustainable biotechnological tool for improving stress tolerance in lilies and enhancing floricultural productivity under climate-challenged environments.