关键词: 盐胁迫, 榉树, 丛枝菌根真菌, 光合特性, 光响应模型

Abstract:

【Objective】 In recent years, the area of land salinization has been increasing with the impact of human activities and climate change. Excessive levels of soil salinity may lead to several ecological problems such as soil dispersion, soil salinization, desertification, destruction of vegetation communities, and reduction of biodiversity. As such, soil salinity is an important environmental factor limiting the continuing development of agriculture and forestry. As a crucial part of terrestrial ecosystems, arbuscular mycorrhizal fungi (AMF) play an important role in the management of saline-alkali land, while Zelkova serrata is a tree species with considerable economic and landscape value in China. Both species have wide application prospects in saline-alkali land forestry production. However, most existing research has focused on the physiological and biochemical characteristics and salt tolerance of Z. serrata, while few have investigated the effects of AMF on the photosynthetic characteristics of salt stressed Z. serrata. Moreover, there is a lack of research on the applicability of the light response model under this condition. Accurate characteristic parameters provided by a suitable light response model may directly or indirectly reflect the photosynthetic physiological process of plants, and offer considerable guidance for forestry production in saline-alkali land. As such, this study investigated the effects of arbuscular mycorrhizal fungi inoculation on the growth and photosynthetic characteristics of Z. serrata, and the applicability of light response model under salt stress. In summary, the objective was to provide a theoretical basis to use mycorrhizal combination technology to improve plant productivity in saline-alkali land.【Method】 Initially, Z. serrata seedlings that were not colonized with AMF were cultivated through seed and substrate sterilization. This was carried out concurrently while three AMF [i.e., Glomus mosseae separated from Bijie, Guizhou (GM₁), G. mosseae separated from Chuxiong, Yunnan (GM₂) and G. tortuosum separated from Ejin Horo Banner, Inner Mongolia (GO)], were multiplied in the artificial climate room for three months. Z. serrata seedlings with consistent growth were transplanted to the greenhouse of Nanjing Forestry University Xiashu Forestry Farm for the pot experiment and four inoculation treatments were established: (1) not inoculated with mycorrhizal fungi (N); (2) inoculated with GM₁; (3) inoculated with GM₂; and (4) inoculated with GO. After one year of AMF colonization and plant growth, potted Z. serrata seedlings of GM₁, GM₂, GO and N treatments were divided into two groups, and subjected to salt stress and non-salt stress treatments, respectively. In the salt stress treatment, 300 mL of 100 mmol/L NaCl solution was poured into each pot every week, and sterile distilled water was used to replace the NaCl solution in the non-salt stress treatment. The treatment was carried out for two months, during which the Hoagland (reduced phosphorus) nutrient solution was regularly replenished. Then, three pots were selected from each treatment to determine the photosynthetic characteristics and mycorrhizal colonization rate. The effect of AMF on the net height growth, net basal diameter growth, net photosynthetic rate, intercellular CO₂ concentration, stomatal limit value, and water use efficiency of Z. serrata under salt stress was explored by comparing and analyzing differences between treatments. The applicability of five kinds of light response models was evaluated by plotting the light response curve and comparing the fitting accuracy of each model in each treatment. 【Result】 There were four key findings from the results. First, the mycorrhizal colonization rate of the GM₁ and GO treatments decreased significantly under salt stress. Second, salt stress had a significant inhibitory impact on the net height growth and ground diameter growth of Z. serrata, while the GM₁ and GM₂ treatments significantly increased the net ground diameter growth under salt stress. Third, under salt stress, there was a clear decrease in the net photosynthetic rate of Z. serrata. All three treatments could increase the net photosynthetic rate, stomatal limit value, and water use efficiency, while reducing intercellular CO₂ concentration. Among the treatments, the GM₂ and GO treatments exhibited the largest changes compared with the N treatment. Fourth, only the average R² fitted by the Ye Zi-Piao model was >0.900 under salt stress, and the R² of the other four models were <0.900. 【Conclusion】 Salt stress was likely to inhibit plant growth and photosynthetic characteristics. Inoculation with AMF may promote plant growth, improve the net photosynthetic rate of plant leaves, and alleviate the inhibition of salt stress on plant growth and photosynthetic characteristics. Based on the influence of arbuscular mycorrhizal fungi inoculation on the growth and photosynthetic characteristics of Z. serrata, the GM₂ was prominent; this was recommended as the strain for forestry production in saline-alkali land. Among the five light response models, the Ye Zi-Piao model exhibited the best fitting effect, representing the optimal model to explore the effect of AMF on the net photosynthetic rate of salt stressed Z. serrata.

Key words: salt stress, Zelkova serrata, arbuscular mycorrhizal fungi(AMF), photosynthetic characteristics, light response model