| Myrica rubra is a specialty subtropical fruit tree in China. Naturally, its roots can be infected by Frankia to form the symbiotic nitrogen fixing nodules, which can both improve the soil fertility and the vigor of the plant. Therefore, it is a natural fertilizer wood. Myrica rubra fruit has good flavor and rich nutrition, and are very beneficial to our health, appealing a large number of consumers.In recent years, with the increase of industrial waste emissions and the extensive use of pesticides and chemical fertilizers, the heavy metal pollution in agriculture soil is increasing, among which Pb pollution is particularly prominent. Pb, a toxic pollutant, not only hinders crop growth and quality, but also impairs our health via the food chain.Arbuscular mycorrhizal fungi (AMF) have been shown to improve mineral nutrition, promote growth and development of host plants. AMF also can mitigate drought, salinity, temperature stresses, and improve the resistance ability of plants to pest and disease, so it has great application potential in agricultural production.This experiment was carried out to examine the effects of dual inoculation of Frankia and different AMF strains on the growth of one-year Myrica rubra seedlings. AMF strains are G. intraradices, G. mosseae, A. scrobiculata. By measuring some morphological and physiological indicators, we screened out the best combined inoculation treatment for the growth of Myrica rubra seedlings. On this basis, we have furtherly explored interaction between Frankia and different AMF strains and their effects and physiological mechanism on Pb tolerance of Myrica rubra seedlings under Pb stresses at five levels:3mmol/L,3mmol/L,6mmol/L,9mmol/L,12mmol/L, 15mmol/L, at the same time, setting a control under normal conditions at Ommol/L. The main contents and results in this study are as follows:1. Under normal conditions, the combined inoculation of Frankia and three kinds of AMF strains could increase the plant height, stem diameter, leaf number, nodule amount and nitrogenase activity, promote mineral nutrient absorption, increase N, P, K, Ca content, enhance photosynthesis, thus significantly promote the growth of Myrica rubra seedlings. By comprehensive comparison, G. mosseae was screened out as the best strains for Myrica rubra seedlings.2. Under Pb stress, compared with singte-Frankia treatment, the plant height and leaf relative water content are elevated in Myrica rubra seedlings dual-inoculated. The combined inoculation treatments could also promote mineral nutrient absorption, increase N, P, K, Ca content and enhance photosynthesis, moreover, decrease the accumulation of Pb. Thereby, AMF and Frankia dual-inoculation could greatly enhance tolerance of Myrica rubra seedlings under high Pb stress.3. Under different level of Pb stress, compared with single-Frankia treatment, the combined inoculation treatments could significantly increase the soluble sugar content and soluble protein content, decrease the relative electric conductivity and MDA content, thereby alleviate the oxidative damage caused by Pb stresses. The combined inoculation treatments could also significantly improve the activity of antioxidant enzymes such as SOD, POD and CAT so as to increase the ability of scavenging oxygen free radicals and alleviate the oxidative damage by membrane lipid peroxidation.Results showed that compared to the control (single-inoculated with Frankia), the treatments dual-inoculated with Frankia and three kinds of AMF, especially G. mosseae and A. scrobiculata, could significantly promote plant growth under normal conditions and greatly enhance tolerance of Myrica rubra seedlings under high Pb stress. Therefore, those two AMF could be applied to production practice of Myrica rubra. The results could provide a solid theoretical foundation and practical significance for the applings. |
