Abstract
Pinus massoniana Lamb. is one of the most sensitive species to acid deposition among forest woody plants, but differences in acid resistance among pine families still exist. It is of great significance to study the differences in acid resistance of Masson pine families and to analyze the physiological regulation mechanism of their acid resistance. In this study, the 100-day-old seedlings of 16 Masson pine families were treated with the simulated acid rain (SAR) at different pH levels (5.6, 4.5, 3.5 and 2.5) for 100 days to investigate the plant morphology, chlorophyll content, and root physiological responses. Results showed that pine family No. 35 maintained the good morphology, high chlorophyll content and organic acids secretion, and low plasma membrane permeability exposed to SAR, while family No. 79 presented the opposite. SAR not only increased the root plasma membrane permeability, but also induced an exudation of organic acids from the pine roots, and the test parameters changed sharply when the SAR pH was lower than 4.5. The results indicated that Masson pine could resist to acidic environment (pH 4.5–5.6), and family No. 35 had the acid resistance while the family No. 79 was sensitive to acid stress. The acid resistance diversity of different pine families had close relation with the root physiological processes, including the root plasma membrane permeability and organic acids secretion. For the future research, the natural genetic variation of Masson pine in response to acid stress and its acid resistance mechanism should be further studied.
Highlights
The rapid growth of economy and population has resulted in the excessive consumption of fossil energy, and it increased the emission of S Ox and N Ox, leading to the atmospheric acid deposition
Large-scale observations showed that the regions that are seriously polluted by acid deposition are concentrated mainly in the south and the southwest of China, especially in city-clusters such as the Yangtze River Delta area, the Pearl River Delta area, and the Sichuan B asin[13]
The length of roots and shoots (Fig. 1A,B), the dry weight of roots (Fig. 1C), and the number of primary lateral roots (Fig. 1D) showed different degrees of decrease with the decrease of pH value of simulated acid rain (SAR), the pine morphology was slightly effected by the SAR at pH 5.6–4.5, while under the acid rain gradient of pH 2.5–3.5, the pine morphology indexes decreased obviously
Summary
The rapid growth of economy and population has resulted in the excessive consumption of fossil energy, and it increased the emission of S Ox and N Ox, leading to the atmospheric acid deposition. The soil acidification and the release of soil base ions caused by acid rain erosion can seriously damage plant roots, such as inhibiting root elongation and reducing the number of lateral roots[7], thereby weakening their ability to absorb and transport water and n utrients[11]. Masson pine (Pinus massoniana Lamb.) is a native tree species in China with a wide distribution range and large forest area It is characterized by drought resistance, rapid growth, strong adaptability and high economic value and is a pioneer tree species for afforestation and reforestation[12]. Zhang et al.[22] (2018) found that citric acid and fumaric acid significantly stimulated Hansschlegelia zhihuaiae S113 colonization on cucumber roots, which allowed for improved cucumber growth Both the types and contents of organic acids secretion are affected by plant environmental stress and plant s pecies[23]. Studying the organic acids secretion of Masson pine families with different acid resistance under acid deposition is very important to further understand the physiological mechanism of plant acid resistance
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