Effect of Acid Stress on Physiological Characteristics of Hedera nepalensis var. sinensis

Using one-year-old Hedera nepalensis var. sinensis cuttings as the hydroponic materials, setting 3 treatments with different degree of acid stresspH 6.0 (CK), pH 5.0 and pH 4.0 for 15 days. The objective was to examine the variations in physiological and biochemical indicators, aiming to elucidate the physiological responses of H. nepalensis var. sinensis to diverse levels of acid stress and its mechanisms of tolerance under such stress. The results showed that compared with CK, the contents of photosynthetic pigments, stomatal conductance, net photosynthetic rate, transpiration rate were decreased significantly under acid stress. The non-photochemical quenching coefficient, electron transfer rate were all significantly reduced. The contents of of proline, soluble protein and sugar increased markedly. In addition, the activities of peroxidase, ascorbate peroxidase, catalase, superoxide dismutase, malondi-aldehyde were also increased markedly under each acid treatment. In this experiment, the intensification of acid stress leads to damage in the photosynthetic system, which weakens both the photochemical efficiency and electron transfer rate. Additionally, it reduces the content of photosynthetic pigments. Concurrently, the lipid peroxidation reaction becomes more intense, increasing the accumulation of MDA. The H. nepalensis var. sinensis plants can adapts to acidic environments by elevating the activities of antioxidant enzymes and the content of osmoregulatory substances.