Drought acclimation and the morphology of mycorrhizal Rosa hybrida L. cv. 'Ferdy' is independent of leaf elemental content

Rosa hybrida L. cv. 'Ferdy' is a low maintenance landscape plant which is considered drought resistant. To determine the effects of endomycorrhizae on plant water relations and growth, rooted cuttings of uniform size were established in containers under moderately high P fertilization. Vesicular-arbuscular (VA) mycorrhiza inoculated and noninoculated plants were placed under three water regimes: drought acclimated, non-acclimated and later exposed to drought, or non-stressed. Acclimated plants were conditioned by four 3-d and three 4-d drought cycles. Non-acclimated plants received water daily prior to a single 4-d drought cycles, and non-stressed plants were watered daily throughout the study. Under water deficits, non-acclimated plants had lower leaf water potentials (Ψ_L ), transpiration rates (E) and stomatal conductances (g), than acclimated or non-stressed plants. Non-acclimated plants also had a greater leaf area, leaf number and shoot dry weight than acclimated plants, yet had a comparable leaf area ratio (LAR) and root-shoot ratio. Mycorrhizal plants had a higher E, than non-mycorrhizal plants, even though non-mycorrhizal plants were of comparable biomass (leaf area, shoot and root dry weight and LAR). However, the root-shoot ratio was greater with mycorrhizal plants which had fewer leaves (due to abscission), and lower cuticle and epicuticular wax weights than non-mycorrhizal plants. There was no affect of VA mycorrhiza on leaf osmotic potential (Ψ_n ) stomatal density, leaf cell density, leaf area, or macronutrient uptake. Acclimation of this low-maintenance landscape rose cultivar to water deficits and the mechanism of drought avoidance via leaf abscission, were as beneficial to drought resistance as was mycorrhizal symbiosis.