Effects of Calcium on the Growth and Physiological Characteristics of Camellia oleifera under Aluminum Stress

Abstract

【Objective】The study aims to investigate the effects of calcium on the growth and physiological characteristics of Camellia oleifera seedlings under aluminum stress, with a view to providing theoretical basis for revealing the physiological mechanism of calcium alleviation of aluminum stress in C. oleifera.【Method】The effects of different calcium concentrations (0, 0.5, 1.5, 3 and 5 mmol/L) applied under aluminum stress (4 mmol/L) on the growth, leaf photosynthesis, root osmoregulatory substances and antioxidant enzyme activities of C. oleifera seedlings were determined through a pot experiment.【Result】Aluminum stress inhibited the growth of C. oleifera seedlings significantly, and the application of 3 mmol/L calcium significantly alleviated the inhibition of aluminum growth in C. oleifera, and the plant dry weight increased by 40.58%. For photosynthetic parameters, aluminum stress reduced chlorophyll a, chlorophyll b, carotenoids and total chlorophyll contents of C. oleifera leaves. Net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) decreased by 32.28%, 51.02% and 53.91%, respectively, compared with those under CK treatment, while intercellular CO2 concentration (Ci) increased by 20%. The addition of appropriate amount of calcium (1.5-3 mmol/L) significantly increased the photosynthetic pigment content, Pn, Gs and Tr, and decreased Ci of leaves. Compared with aluminum stress, calcium application could reduce the accumulation of root free proline and increased the soluble sugar content effectively. Under aluminum stress, the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) in the roots and ascorbate peroxidase (APX) in the leaves were significantly reduced. The plasma membrane permeability and malondialdehyde (MDA) content in the roots were significantly increased. Calcium application significantly enhanced antioxidant enzyme activities. POD and AXP activities were highest when the calcium concentration was 1.5 mmol/L, which were 35.13 and 234.11 U/g, respectively; and SOD and CAT activities were highest when the calcium concentration was 3.0 mmol/L, which were 533.20 and 48.42 U/g, respectively. Meanwhile, the addition of appropriate concentration of calcium (1.5-3 mmol/L) significantly reduced root plasma membrane permeability and MDA content, which were 19.52%-31.40% and 23.32%-27.86% lower than those under aluminum stress treatment, respectively.【Conclusion】Calcium at moderate concentrations (1.5-3 mmol/L) significantly improved photosynthetic capacity and antioxidant enzyme activity of C. oleifera leaves, reduced reactive oxygen stress and production of membrane lipid peroxidation products, and alleviated the toxic effects of aluminum stress on C. oleifera seedlings by regulating osmotic substances. However, when the calcium concentration reached 5 mmol/L, it inhibited the growth of C. oleifera seedlings.

Keywords

• camellia oleifera
• aluminum stress
• calcium
• physiological characteristics
• photosynthetic parameter