Abstract
The soils in karst regions, with carbonate rocks as the background material, are characterized by two main factors, drought and high calcium levels. Handeliodendron bodinieri (Levl.) Rehd is an endemic plant species in this area of China. However, few studies have been carried out on the adaptation mechanism of H. bodinieri to drought and high calcium soil. To reveal the physiological responses of H. bodinieri to exogenous calcium under drought stress, 10% PEG-6000 was used to simulate drought stress, and the effects of exogenous calcium at different concentrations on the physiology of H. bodinieri seedlings under drought stress were studied. The results showed that drought stress significantly reduced the relative water content and water potential of H. bodinieri seedlings. Malondialdehyde (MDA) content, O2− and H2O2 production rates significantly increased under drought stress. The addition of exogenous calcium significantly reduced MDA content and O2− and H2O2 production rates. Moreover, peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), ascorbic acid peroxidase (APX) and glutathione peroxidase (GPX) activities increased significantly under drought stress. At the same time, the accumulation of osmotic regulators such as soluble sugar, betaine and free proline also increased significantly. The addition of exogenous calcium further increased the activity of antioxidant enzymes and the accumulation of osmotic regulatory substances. Consequently, the oxidative stress and osmotic stress induced by drought decreased. Finally, exogenous calcium enhanced the photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) of H. bodinieri under drought stress and significantly improved water use efficiency (WUE). This study confirmed that the application of exogenous calcium can enhance the water condition, photosynthetic capacity, osmotic regulation and antioxidant capacity of H. bodinieri under drought stress. Of the treatments, the 10 mmol·L−1 CaCl2 treatment is more likely to improve survival of H. bodinieri under drought tolerance. This study provides an important reference for describing the adaptation mechanism and appropriate conservation of H. bodinieri under drought and high calcium conditions.
Highlights
The karst region in China is approximately 3.44 million km2, which is the most concentrated area of karst globally [1]
H. bodinieri leaves treated with different concentrations of exogenous calcium were always higher than that those treated without exogenous calcium
The results showed that water deficit led to a decrease in the water status and photosynthetic capacity of the leaves, and the degree of oxidative stress increased
Summary
The karst region in China is approximately 3.44 million km , which is the most concentrated area of karst globally [1]. In this area, the soil layer is shallow and discontinuous, and the rock exposure rate is high. The soil is rich in calcium and is alkaline, with a high infiltration rate, and the ecological environment is extremely fragile [2]. In the karst region in southwestern China, an area of 12 × 104. The available soil moisture in karst areas can only meet transpiration requirements for one to two weeks after the plant is saturated at field moisture capacity [5]. Drought stress has become one of the main factors restricting the growth of karst habitats
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