Effects Of Arbuscular Mycorrhizal Fungi(AMF) On Drought Resistance Of Glycine Max Under Different Water Conditions In Soil From Karst Area

Using soybean (Glycine max) as research material, a potted experiment was conducted to explore the effects of Glomus mosseae (G.m) and Glomus constrictum (G.c) on drought resistance in two typical karst soil (alkaline soil and acid soil). The results show as follows:1. Under drought stress, the infection intensity (M%), infection frequency (F%) and arbuscular abundance (A%) of soybean root system inoculated with AMF were significantly decreased than that with normal water condition. On the contrary, comparing to no-AMF and drought treatment, the three infection rate indexes (M%, F%and A%) of soybean with AMF and drought treatment increased significantly; Comparing infection rate between two AMF species, no matter what kind of soil and water condition, the three infection rate indexes of soybean with G.m and drought treatment were more higher than that with G.c and drought treatment; Moreover, comparing infection rate between two typical karst soil, no matter what kind of AMF and water condition, the three infection rate indexes of soybean in acid soil were more higher than that in alkaline soil.2. Under drought stress, comparing to no-AMF treatment, the relative water contents of soybean inoculated with different AMF were increased significantly (P≤0.05).And the water holding capacity of soybean with G.m was stronger than with G.c, especially in acid soil.3. In alkaline soil and acid soil, the accumulation of superoxide anion free radical (SAFR) and malondialdehyde (MDA) of soybean with AMF under drought condition showed the tendence that:the cumulative amount of SAFR and MDA under drought stress without AMF treatment were the highest than that with G.c plus drought stress treatment and that with G.m plus drought stress treatment respectively, the cumulative amount of SAFR and MDA with G.m plus drought stress treatment were the lowest.Comparing cumulative amount of SAFR and MDA between two typical karst soil, that in acid soil were more lower than that in alkaline soil. Regarding the accumulation of SAFR, it showed significant differences among treatments with different AMF; For accumulation of MDA, there had no significant differences among treatments with different AMF; The trend of activity changes of protective enzyme of soybean, such as superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) indicated that: activities of3protective enzyme with G.m under drought stress> that with G.c under drought stress> that without AMF under drought stress. Inoculated with the same AMF, the activity changes of SOD,POD,CAT represented: Activities of3protective enzyme in acid soil> that in alkaline soil, and the differences of treatment were significant(P≤0.05).4. Under drought stress, comparing to no-AMF treatment, contents of free proline and soluble sugar with AMF treatment increased in different degree. Similar to change trend of SOD activity, content changes of free proline and soluble sugar with AMF treatment showed:that with G.m under drought stress> that with G.c under drought stress> that without AMF under drought stress,that in alkaline soil>that in acid soil.The differences of treatment were significant too (P≤0.05).5. Similar to change tendence of SOD activity, the activity of nitrate reductase (NR) with G.m under drought stress was higher than that with G.c under drought stress and that without AMF under drought stress. The activity of NR without AMF under drought stress was the lowest. Inoculated with the same AMF, the activity changes of NR in acid soil was higher than that in alkaline soil, and the differences of treatment were significant (P≤0.05). As for soluble protein, similar to change trend of MDA accumulation, content of soluble protein with AMF under drought treatment decreased significantly than that with no-AMF under drought treatment. Under drought stress, the content of soluble protein with G.m<that with G.c. And comparing two typical karst soil, the content of soluble protein in acid soil<that in alkaline soil.6. Under the water stress,comparing with drought treatment without AMF, the content of chlorophyll, intercellular CO2concentration and photosynthetic rate as well as the transpiration rate and stomata conductance of soybean all increased significantly, the change tendency of the5indexes above were similar to that of SOD. The differences of same index with different treatments were significant (P≤0.05).7. Comparing with drought treatment without AMF, the biomass (dry weight of the whole plant) and grain yield of soybean with AMF and drought treatment increased significantly.The change trend of biomass and grain yield indicated:that with G.m under drought stress> that with G.c under drought stress> that without AMF under drought stress. In another word, soybean which inoculated with G.m in the acid soil had highest biomass and grain yield under drought stress.Furthermore, biomass and grain yield of soybean in acid soil>that in alkaline soil.The differences of same index with different treatments were significant(P≤0.05).Anyhow, under drought stress, compared with treatment without AMF, soybean inoculated with AMF had a high NR activity. Accompanied by the decrease of SAFR and MDA content, protective enzyme activity and the amount of osmotic regulation substance (free proline and soluble sugar) enhanced. The facts mentioned above result in better water retention capacity and mineral nutrient absorption ability,as well as alleviation of the drought injury. Then the drought resistance of soybean improved, metabolic activity such as photosynthesis maintained a high level.Finally, the biomass and grain yield of soybean enhanced.Moreover, under drought condition, the promoting effect on drought resistance and growth of soybean with G.m was higher than that with G.c. It drew a conclusion that Glomus mosseae(G.m) can be used as one of the dominant candidate fungi for improving water holding ability,biomass and grain yield of soybean in the karst areas.