Introduction
At present, soil salinization has become an increasingly severe ecological and environmental problem worldwide (Ustun et al., 2018; Litalien and Zeeb, 2020). The growth and development of plants in saline land was affected by destroying chloroplast structures and cell membranes (Zhuang et al., 2019), weakening of photosynthetic capacity (Yang et al., 2020), causing various metabolic disorders (Forni et al., 2017). Some plants exposed to salt stress will produce physiological mechanisms to adapt to the new environment (De Oliveira et al., 2022). However, the salt tolerance mechanism of plants is very complicated. Therefore, studying the physiological and ecological characteristics in the response to salt stress can help understand the sensitivity and resistance of plants and provide useful information for further introduction and cultivation in saline soil areas. In recent years, some scholars have studied the effects of salt stress on plants, but most focused on field crops (Thi Thu et al., 2020) and horticultural crop (Miao et al., 2020; Zhang et al., 2020). Research indicates that Tamarix hispida has the potential to remediate soil saline-alkali (Xie et al., 2023). Catalpa bungei mainly resists from saline-alkali stress by accumulating contents of soluble sugars and proline improving SOD enzymatic activity and photosynthesis (Gao et al., 2023), Quercus chenii could adapt to NaCl stress with a concentration below 3‰, and this concentration could be used as the critical reference concentration for the promotion of Q. chenii seedlings in the coastal regions of Jiangsu (Liu et al., 2023).
Many studies showed that trees played a very important role in the transformation of saline-alkali land (Xu et al., 2020). Therefore, it is necessary to focus studies of salt tolerance on trees and their related physiological characteristics to improve the utilization of saline-alkali land.
Many species of the Acer genus are important decorative trees throughout the world because of their attractive leaf colours and shapes (Wada and Ribbens, 1997). Acer ginnala and Acer palmatum are widely distributed species, mainly found in Japan, Korea, Mongolia, East Russia, and China (Dong et al., 2019). They not only have a high ornamental value but also economic value. There were some studies on the physiological characteristics of salt stress (Li et al., 2020), however, these studies mainly focused on the physiological response to different concentrations of NaCl. In the natural environment, the salts in soil are mainly neutral (NaCl and Na2SO4) and alkaline (Na2CO3 and NaHCO3) (Yin et al., 2019). Different types of salt stress have different effects on plant growth and physiology. Some scholars have studied the effects of mixed stress with Na2CO3 and NaHCO3 on the seed germination, seedling growth, and physiological characteristics of Clematis (Zhang et al., 2022) and Chenopodium quinoa (Wang et al., 2021). However, there are no reports yet on the response of maple trees to mixed saline-alkali stress with Na2CO3 and NaHCO3.
The purpose of this study was to clarify the physiological effects of combined NaCl and NaHCO3 stress on the seedlings of two maple species and evaluate the salt tolerance of two maples. The study results have important scientific significance and practical value in understanding the adaptability of maple trees, improving the utilization value of saline-alkali land, and guiding the planting and management of maple trees.
