Effects Of AM Fungi On Salt Resistance Of Different Types Of Halophytes

After establishing the symbiosis between arbuscular mycorrhizal (AM) fungi and plant roots, they form huge mycelium network in the soil, which plays an important role in the exchange of nutrients, energy flow, and signal substance transportation among organisms, maintaining soil microbe-flora equilibrium and stability, increasing biodiversity and ecosystem stabilization. It suggested that, AM fungi were able to resist salt stress because of their wide distribution in all kinds of saline soil. AM fungi can regulate many physiological and biochemical metabolisms in plants, which is very significant in salt resistance of plants.It is predicted that saline soil threatens seriously sustainable development of the environment and agriculture, forest, animal husbandry production, which become global problems. Thus, many countries in the world are studying on the techniques to remedy and modify saline soils. At present, biological measures are paid more and more close concern because of their less input, greater efficiency and more benefits, the purpose of which is to screen out excellent organism which is adapted to high saline environment. The organisms can be used to exploit and utilize saline soil. Lots of work in improving plant adaptive ability and productivity in saline siol by making use of mycorrhizal fungi showed great progress. However, many past works were not systematic and comprehensive. Further research is required urgently to elucidate the mechanisms involved at molecular level. In this experiment, Suaeda salsa L, Limonium sinense and Glycine soja Leguminosae were used as host plants and Glomus mosseae, Glomus versiforme and Gigaspora margarita were employed as inoculating fungi. From trying on optimal combination between different NaCl concentration and different AM fungi and doing experiments under different NaCl concentration based on the optimal combination, we primarily investigated the effects of AM fungi and NaCl stress on different halophytes and the effects of AM fungi on halophytes under different NaCl treatment, which made for choosing optimal combination between AM fungi and halophytes and the optimal NaCl concentration beneficial to bringing the function of AM fungi into play. Then, based on the optimal condition, the relative indices such as biomass, the content of MDA, K~+, Na~+ and Cl~- , the activity of SOD and CAT and analysis of spectrum of SOD and CAT isoenzyme are determined to elucidate the possible mechanism of AM fungi enhancing resistance of halophyte to higher salt stress. The main results are as follows:1. The most suitable AM fungi species of Suaeda salsa L and Glycine soja Leguminosae was Glomus mosseae and Gigaspora margarita, respectively, and the optimal NaCl concentration was 400 mmol/L and 200 mmol/L, respectively. Surprisingly, under conditions of control and salt stress, the efficiency of the tested AM fungal colonization on Limonium sinense was low, and AM fungi could not work. Hence, there were no significant effects of AM fungi on Limonium sinense resistance to salt stress under the greenhouse conditions.2. AM fungi could significantly increase Suaeda salsa L plant height, numbers of leaves and branches, shoot inorganic dry weight and root fresh weight, organic and inorganic dry weight, length of roots, and promote remarkably significant increase of shoot fresh weight and organic dry weight. With increasing of NaCl treatment time, colonization rate of AM fungi significantly decreased.3. With increasing of NaCl treatment time, the leaf content of MDA of inoculation treatment and non-inoculation treatment increased. But increase degree of inoculation treatment was less than that of non-inoculation control. Moreover, at the same treatment day, the content of MDA of inoculation-treated plants is significantly lower than that of non-inoculation controls. The decrease degree showed that at 14th day of NaCl treatment, the improving function of AM fungi was the best.4. With the increase of NaCl concentration, the content of K~+ and K/Na ratio in shoot and roots decreased, whereas the content of Na~+ and Cl~- was markedly increased. However, at the same concentration of NaCl treatment, the content of K~+ and K/Na ratio of inoculation-treated plants increased significantly compared with that of non-inoculation control. The content of Na~+ and Cl~- in shoot was significantly less than control, but the situation in the roots was reverse. With increasing of NaCl treatment time, the activity of SOD and CAT of inoculation-treated and control plant leaves showed the same trend, namely, increasing at first and then declining. But the increase and decrease degree of inoculation-treated plants was higher and lower than that of non-inoculation controls, respectively. At the same concentration of NaCl treatment day and NaCl concentration, the activity of SOD and CAT of inoculation-treated plants increased compared with that of non-inoculation control, whose increase degree behaved significantly or remarkably significant, which took on only at 14 days and 21 days when CAT was determined. After 14 days NaCl treatment, the improving function of AM fungi was the best. The analysis of isoenzymes of SOD and CAT in the leaves at 14 days showed that Fe-SOD, Cu/Zn-SOD1, Cu/Zn-SOD2 and CAT1, CAT2 of inoculation-treated plants were higher than those of non-inoculation controls.5. These results suggest that AM fungi could improve salt tolerance of halophytes by enhancing the activity of SOD and CAT in the leaves, regulating the balance of ion and reducing the leaf content of MDA. Further research is urgently required to elucidate the mechanisms of AM fungi-mediated increase of salt tolerance of halophytes at molecular level.