[Aluminum absorption capacity of different cultivars of Hydrangea macrophylla seedlings under aluminum stress and the physiological and biochemical mechanisms].

Hydrangea macrophylla exhibits strong tolerance to acid and aluminum stress. Many cultivars can absorb Al³⁺ from soils, resulting in variations of their flower color from red to blue. This characteristic presents a potential avenue for the ecological remediation of aluminum-rich acidic soils. To assess the capacities of aluminum absorption among different cultivars, we utilized the cutting seedlings of 45 popular H. macrophylla cultivars via hydroponic culture, which were treated under 0 (control) and 800 μmol·L^-1 Al₂(SO₄)₃. The aluminum absorption abilities were determined through root tip staining and aluminum content determination methods. We selected two representative cultivars with the strongest or weakest aluminum absorption capacities for further investigation of the physiological and biochemical mechanisms under aluminum stress. The results showed that the 45 cultivars could be categorized into five levels according to their aluminum absorption capacities: strong, relatively strong, intermediate, relatively weak, and weak, comprising 2, 11, 15, 15, and 2 cultivars, respectively. Amongst them, Bailer and White angel were identified as representative of strong and weak aluminum absorption capacities, respectively. In comparison to White angel, the aluminum-treated Bailer exhibited significant increases in chlorophyll content, transpiration rate, net photosynthetic rate, intercellular CO₂ concentration, and stomatal conductance with significant increase of 24.8%, 63.9%, 11.2%, 9.2%, and 66.7%, root length, root surface area, root volume, and root tip number increased by 4.7%, 2.9%, 14.3%, and 7.8%, the activities of antioxidant enzymes (peroxidase, catalase, and superoxide dismutase), and the contents of soluble sugar and soluble proteins exhibited significant increases by 88.4%, 35.3%, 7.7%, 2.4%, and 21.7% in the roots, and 78.4%, 103.7%, 101.1%, 138.9%, and 18.1% in the leaves, respectively. These findings suggested that Bailer could effectively mitigate damage from Al stress by enhancing photosynthesis, antioxidant enzymatic activities, and nonenzymatic antioxidants, thereby improving its aluminum absorption ability and tolerance, which has the potential application in the remediation of aluminum-rich acidic soils.